Difference between revisions of "PEERS"

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The Penn Electrophysiology of Encoding and Retrieval Study is a multi-session experiment looking at scalp EEG during free recall and recognition. We recruit both younger adults (16-30) and older adults (60-90) for 22 or 9 sessions, respectively.
+
The '''Penn Electrophysiology of Encoding and Retrieval Study (PEERS)''' is a series of studies carried out between 2010 and 2020 to elucidate the EEG correlates of memory processes with a particular focus on retrieval dynamics in free recall.   In conducting PEERS we set out to do an experiment in ''big science'' where many subjects (over 150 in PEERS1-3 and 98 in PEERS4) each contributed a large quantity of data (e.g., 6-8 sessions each in PEERS1-3, and 24 sessions in PEERS4) allowing for detailed analysis of individual subject behavior and physiology.
  
Please see the [[#How to get involved|information below]] if you are interested in volunteering for this study.
+
The PEERS dataset in its entirety (experiments 1-5) is available [https://openneuro.org/datasets/ds004395/versions/2.0.0 here on OpenNeuro] in [https://bids.neuroimaging.io BIDS] format (see [https://openneuro.org/datasets/ds004395/versions/2.0.0/download instructions for downloading]). This dataset is about 8.7 TB, which means it cannot fit on disk for most laptops, so it is recommended to work with partial downloads unless you have access to an HPC or a desktop with large disk space. We recommend using DataLad to manage downloading subsets of the data while retaining the full file tree - see [https://handbook.datalad.org/en/latest/usecases/openneuro.html this tutorial].
  
== Information for volunteers ==
+
The BIDS format opens up access to a whole suite of open-source software tools for data processing and analysis. See a comprehensive list of software and integrations  [https://bids.neuroimaging.io/benefits.html#software-currently-supporting-bids here]. Of particular note are integrations with [https://mne.tools/mne-bids MNE-python] and [https://eeglab.org/tutorials/04_Import/BIDS.html EEGLAB]. [https://bids-apps.neuroimaging.io BIDS Apps] are a series of neuroimaging pipelines that work out of the box with BIDS-formatted data.
===Studying the brain===
+
  
At the Computational Memory Lab, we use brain recordings to better understand how human memory works. We are devoted to learning how people form and retrieve memories. Eventually, we hope this information will be used to improve the lives of people with brain disorders and restore normal memory function to those who have lost it.  
+
The PEERS1-3 behavioral dataset, in a lab-specific format with some additional fields generated during post-processing, can be downloaded directly [https://memory.psych.upenn.edu/files/PEERS.data.tgz here]. As this dataset is substantially smaller, it may appeal to those not analyzing brain data.  
 
+
<!-- Please see [[Data Archive]] for behavioral datasets used in individual publications, and [[Electrophysiological_Data | our electrophysiological data portal]] for brain data.  To aid in the reproducibility of results reported in individual publications, we have shared the specific datasets used in each paper along with the paper itself. -->
===About our tasks===
+
 
+
The Penn Electrophysiology of Encoding and Retrieval Study focuses on episodic memory. This is your memory for everyday events (including people, places, and things) in time. Because these memories are unique to each person individually, we must find a controlled way to learn about this form of human memory. In this study, we use lists of words, each individual word representing an "episode" in time. Very simply, we will ask you to study lists of words and then recall them in any order.  
+
  
 
<center>
 
<center>
 
<gallery widths=450px heights=350px perrow=2>
 
<gallery widths=450px heights=350px perrow=2>
 
File:ScalpTest.jpg|Our experiment
 
File:ScalpTest.jpg|Our experiment
File:EEGNet.jpg|One of our nets
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File:EEGNet.jpg|One of our nets being worn by Dr. Aswhin Ramayya
 
</gallery>
 
</gallery>
 
</center>
 
</center>
  
===What is EEG?===  
+
<!--
 +
The following publications draw on the PEERS dataset:
 +
* Cohen, R. T. and Kahana, M. J. (2022). A memory based theory of emotional disorders. Psychological Review 129(4), 742–776. [[Publications#CoheKaha21|(more)]]
 +
* Aka, A., Phan, T., and Kahana, M. J. (2021). Predicting recall of words and lists. Journal of Experimental Psychology: Learning, Memory, and Cognition [[Publications#AkaEtal21|(more)]]
 +
* Katerman, B. S., Li, Y., Pazdera, J. K., Keane, C., and Kahana, M. J. (2021). EEG biomarkers of free recall. NeuroImage [[Publications#KateEtal21|(more)]]
 +
* Weidemann, C. T. and Kahana, M. J. (2021). Neural measures of subsequent memory reflect endogenous variability in cognitive function. Journal of Experimental Psychology: Learning, Memory, and Cognition [[Publications#WeidKaha21|(more)]]
 +
* Healey, M. K. and Kahana, M. J. (2020). Age-related differences in the temporal dynamics of spectra power during memory encoding. PLOSone, 15(1). [[Publications#HealKaha20|(more)]]
 +
* Broitman, A. W., Kahana, M. J., and Healey, M. K. (2019). Modeling retest effects in a longitudinal measurement burst study of memory. Computational Brain & Behavior. [[Publications#BroiEtal19|(more)]]
 +
* Weidemann, C. T. and Kahana, M. J. (2019). Dynamics of brain activity reveal a unitary recognition signal. Journal of Experimental Psychology: Learning, Memory, and Cognition, 45(3), 440–451. [[Publications#WeidKaha19|(more)]]
 +
* Kahana, M. J., Aggarwal, E. V., and Phan, T. D. (2018). The variability puzzle in human memory. Journal of Experimental Psychology: Learning, Memory, and Cognition [[Publications#KahaEtal18|(more)]]
 +
* Kuhn, J. R., Lohnas, L. J., and Kahana, M. J. (2018). A spacing account of negative recency in final free recall. Journal of Experimental Psychology: Learning, Memory, and Cognition [[Publications#KuhnEtal18|(more)]]
 +
* Long, N. M. and Kahana, M. J. (2017). Modulation of task demands suggests that semantic processing interferes with the formation of episodic associations. Journal of Experimental Psychology: Learning, Memory, and Cognition [[Publications#LongKaha17|(more)]]
 +
* Weidemann, C. T. and Kahana, M. J. (2016). Assessing recognition memory using confidence ratings and response times. Royal Society Open Science, 3, 150670. [[Publications#WeidKaha16|(more)]]
 +
* Healey, M. K. and Kahana, M. J. (2015) A four–component model of age–related memory change. Psychological Review. [[Publications#HealKaha15|(more)]]
 +
* Lohnas, L.J. , Polyn, S.M., and Kahana, M. J. (2015) Expanding the role of memory search: Modeling intralist and interlist effects in free recall. Psychological Review, 122(2), 337–363.  [[Publications#LohnEtal15|(more)]]
 +
* Long, N. M., Danoff, M. S., and Kahana, M. J. (2015). Recall dynamics reveal the retrieval of emotional context. Psychonomic Bulletin and Review, 22(5), 1328-1333. [[Publications#LongEtal15|(more)]]
 +
* Healey, M. K., Crutchley, P., and Kahana, M. J. (2014). Individual differences in memory search and their relation to intelligence. Journal of Experimental Psychology: General, 143(4), 1553–1569  [[Publications#HealEtal14|(more)]]
 +
* Healey, M. K. and Kahana, M. J. (2014). Is memory search governed by universal principles or idiosyncratic strategies? Journal of Experimental Psychology: General, 143, 575–596  [[Publications#HealKaha14|(more)]]
 +
* Lohnas, L. J. and Kahana, M. J. (2014a). Compound cuing in free recall. Journal of Experimental Psychology: Learning, Memory and Cogntion, 40(1), 12-24 [[Publications#LohnKaha12a|(more)]]
 +
* Long, N. M., Burke, J. F., and Kahana, M. J. (2014). Subsequent memory effect in intracranial and scalp EEG. NeuroImage, 84, 488–494. [[Publications#LongEtal14|(more)]]
 +
* Lohnas, L. J. and Kahana, M. J. (2013). Parametric effects of word frequency effect in memory for mixed frequency lists. Journal of Experimental Psychology: Learning, Memory, and Cognition, 39(6), 1943–1946.  [[Publications#LohnKaha13|(more)]]
 +
* Miller, J. F., Kahana, M. J., and Weidemann, C. T. (2012). Recall termination in free recall. ''Memory & Cognition'', 40(4), 540–550. [[Publications#MillEtal12|(more)]]
 +
 
 +
(List is current as of August 2022. See [[Publications]] for all lab publications.) -->
 +
 
 +
== PEERS publications ==
 +
<include nopre noesc src="http://memory.psych.upenn.edu/files/pages/peers.html" />
 +
 
 +
== PEERS 1-3 Detailed Methods ==
 +
=== Introduction ===
 +
This section provides a comprehensive overlook of the experimental methods for the PEERS (AKA ltpFR) experiment.
 +
 
 +
ltpFR is a 20 session experiment using scalp EEG technology, with 2 additional behavioral sessions (WAIS and WMS-CVLT). Participants are screened for ltpFR using the [https://memory.psych.upenn.edu/InternalWiki/PyFR pyFR paradigm] in a one session preliminary study. There is a free recall section of the experiment and a recognition section of the experiment. [http://memory.psych.upenn.edu/ltp_reports/LTP_session.pdf View a diagram of the session]
 +
 
 +
For information about how to analyze the LTP data, please see the  [https://memory.psych.upenn.edu/InternalWiki/Scalp_analysis Scalp analysis page].
 +
 
 +
Each of the 20 sessions includes several different tasks: track ball, free recall, final free recall, recognition.
 +
 
 +
===Trackball===
 +
 
 +
Each session begins with the trackball task, which is intended to provide information on the EEG signals characteristic of different types of eye movements. Track ball proceeds as follows:
 +
 
 +
1. Asterisks are drawn at the center of the screen and at 12, 3, 6 and
 +
9 o'clock positions.
 +
 
 +
2. The pre-recorded words "close" and "open" are played in sequence 5
 +
times.  The duration of the "close" and "open" clips are approximately
 +
1480 and 1400 ms, respectively.  Each word is followed by a delay
 +
interval of 5000 ms + uniformly distributed jitter drawn from the
 +
interval [0,300] ms.
 +
 
 +
3. The pre-recorded words "left" and "right" are played in sequence 5
 +
times.  The duration of the "left" and "right" clips are approximately
 +
990 and 920 ms, respectively.  Each word  is followed by a delay
 +
interval of 2000 ms + uniformly distributed jitter drawn from the
 +
interval [0,300] ms.
 +
 
 +
4. The asterisks at the edge of the screen are hidden, and the
 +
asterisk at the center of the screen is caused to trace a curve
 +
defined by a B-spline fit to 10 randomly-selected screen coordinates.
 +
This is followed by a delay of 5000 ms + uniformly distributed jitter
 +
drawn from the interval [0,300] ms.
 +
 
 +
5. The asterisks described in 1. are displayed again.
 +
 
 +
6. The pre-recorded words "up" and "down" are played in sequence 5
 +
times.  The duration of the "up" and "down" clips are approximately
 +
1060 and 1050 ms, respectively.  This is followed by a delay of 5000
 +
ms + uniformly distributed jitter drawn from the interval [0,300] ms.
 +
 
 +
7. Another curve-tracing stimulus is shown as in 4, followed by a
 +
delay with the same parameters.
 +
 
 +
8. The pre-recorded word "blink" is played 5 times.  The duration of
 +
the clip is 695 ms, approximately.  This is followed by a delay of
 +
5000 ms + uniformly distributed jitter drawn from the interval [0,300]
 +
ms.
 +
 
 +
9. The close/open task described in 2. is repeated, with the same
 +
delay parameters.
 +
 
 +
===Free Recall===
 +
Across all sessions, participants study lists of words and recall them. On a subset of lists, participants must perform a size or animacy judgment task. The task type is denoted by color, purple or green, font, and case (i.e, uppercase or lowercase) (assigned randomly for each participant). Participants must decide if the word presented is an object that is SMALL/BIG (can/cannot fit in a shoebox) or LIVING/NONLIVING. The participant is told in advance which color represents which judgment, and this assignment is consistent throughout all 20 of their sessions. For each word, they press one of four labeled buttons on the keyboard to make the appropriate judgment. There are no-task/control lists during which there is no judgment task, task-lists, during which participants perform either a size or animacy judgment on all list items, and switch-lists, during which participants alternate between size and animacy judgments within list.
 +
 
 +
The experiment has three phases, where different sessions had different manipulations, see below. The transition between phases changed after subject LTP209.
 +
 
 +
==== LTP063 to LTP209 ====
 +
 
 +
==== Phase 1: Task Manipulation ====
 +
'''Session 1 (practice)'''
 +
{| class="wikitable"
 +
! Quantity per session
 +
! Task
 +
! Order in session
 +
|-
 +
| 4
 +
| NT
 +
| Lists 1-4
 +
|-
 +
| 4
 +
| Size
 +
| Either 5-8 or 9-12
 +
|-
 +
| 4
 +
| Anim
 +
| Either 5-8 or 9-12
 +
|-
 +
| 4
 +
| Switch
 +
| Lists 13-16
 +
|}
 +
 
 +
'''Sessions 2-7'''
 +
{| class="wikitable"
 +
! Quantity per session
 +
! Task
 +
! Order in session
 +
|-
 +
| 4
 +
| NT
 +
| Random in lists 3-16
 +
|-
 +
| 3
 +
| Size
 +
| Random in lists 3-16
 +
|-
 +
| 3
 +
| Anim
 +
| Random in lists 3-16
 +
|-
 +
| 6
 +
| Switch
 +
| Lists 1-2. remainder random in 3-16
 +
|}
 +
 
 +
==== Phase 2: Distractor Manipulation ====
 +
 
 +
In Phase 2, arithmetic is introduced to the experiment in addition to everything the participant was performing in Phase 1. The arithmetic consists of adding three numbers 1 through 9, inclusive (A + B + C). It is ALWAYs three numbers and always addition. Participants are asked to answer as many math problems correctly as they can (i.e. they should balance speed and accuracy). There are 3 different math lists: inter-item distractor lists, in which the participant does a block of arithmetic before each word in the list; end-of-list distractors, in which the participant does a block of arithmetic after the list/right before the recall period; and no math lists. There is a counter on the top right of the screen, allowing the participant to see the number of correctly answered math problems throughout the session. The list number is reduced during this phase because the math adds additional time to the experiment. Take note: In this phase, there are no control (NT) lists, only 4 switching lists, and 8 single judgement lists (4 BIG/SMALL lists and 4 LIVING/NON-LIVING lists) for a total of 12 lists per session.  Numbers in each cell of the table represent the number of seconds that each distractor type was presented.
 +
 
 +
'''Session 8 (practice)'''
 +
Task: 7 size lists, 7 animacy lists, randomly (not counterbalanced across distractor tasks)
 +
{| class="wikitable"
 +
! Quantity per session
 +
! Inter-item distractor time (s)
 +
! End of list distractor time (s)
 +
! Order in session
 +
|-
 +
| 2
 +
| 0
 +
| 0
 +
| Never list 1, otherwise random
 +
|-
 +
| 4
 +
| 0
 +
| 8
 +
| Random
 +
|-
 +
| 2
 +
| 0
 +
| 16
 +
| Random
 +
|-
 +
| 4
 +
| 8
 +
| 8
 +
| Random
 +
|-
 +
| 2
 +
| 16
 +
| 16
 +
| Random
 +
|}
 +
 
 +
''' Sessions 9-14 '''
 +
Task: 6 switch, 3 size, 3 animacy, randomly (not counterbalanced)
 +
{| class="wikitable"
 +
! Quantity per session
 +
! Inter-item distractor time (s)
 +
! End of list distractor time (s)
 +
! Order in session
 +
|-
 +
| 2
 +
| 0
 +
| 0
 +
| Never list 1, otherwise random
 +
|-
 +
| 3
 +
| 0
 +
| 8
 +
| Random
 +
|-
 +
| 2
 +
| 0
 +
| 16
 +
| Random
 +
|-
 +
| 3
 +
| 8
 +
| 8
 +
| Random
 +
|-
 +
| 2
 +
| 16
 +
| 16
 +
| Random
 +
|}
 +
 
 +
==== Phase 3: Externalized FR ====
 +
 
 +
In Phase 3, participants stop doing arithmetic and return to only doing the judgement task. In the original Phase 3, participants were asked to recall any words that are salient to them in addition to those that they remember seeing from the list. It is important to note that the participants are not doing a stream of consciousness recall in this task, but that they were instructed to recall only words that are particularly salient.
 +
 
 +
'''Sessions 15-20'''
 +
{| class="wikitable"
 +
! Quantity per session
 +
! Task
 +
! Order in session
 +
|-
 +
| 4
 +
| NT
 +
| Random in lists 3-16
 +
|-
 +
| 4
 +
| Size
 +
| Random in lists 3-16
 +
|-
 +
| 4
 +
| Anim
 +
| Random in lists 3-16
 +
|-
 +
| 4
 +
| Switch
 +
| Lists 1-2. remainder random in 3-16
 +
|}
 +
 
 +
==== LTP210 to LTP293 ====
 +
==== Phase 1: Task Manipulation (taskFR) ====
 +
'''Session 1 (practice)'''
 +
{| class="wikitable"
 +
! Quantity per session
 +
! Task
 +
! Order in session
 +
|-
 +
| 4
 +
| NT
 +
| Lists 1-4
 +
|-
 +
| 4
 +
| Size
 +
| Either 5-8 or 9-12
 +
|-
 +
| 4
 +
| Anim
 +
| Either 5-8 or 9-12
 +
|-
 +
| 4
 +
| Switch
 +
| Lists 13-16
 +
|}
 +
 
 +
'''Sessions 2-7'''
 +
{| class="wikitable"
 +
! Quantity per session
 +
! Task
 +
! Order in session
 +
|-
 +
| 4
 +
| NT
 +
| Random in lists 3-16
 +
|-
 +
| 4
 +
| Size
 +
| Random in lists 3-16
 +
|-
 +
| 4
 +
| Anim
 +
| Random in lists 3-16
 +
|-
 +
| 4
 +
| Switch
 +
| Lists 1-2. remainder random in 3-16
 +
|}
 +
 
 +
==== Phase 2: Distractor Manipulation (CDTFR)====
 +
'''Session 8 (practice) '''
 +
Task: 7 size lists, 7 animacy lists, randomly (not counterbalanced across distractor tasks)
 +
{| class="wikitable"
 +
! Quantity per session
 +
! Inter-item distractor time (s)
 +
! End of list distractor time (s)
 +
! Order in session
 +
|-
 +
| 2
 +
| 0
 +
| 0
 +
| Never list 1, otherwise random
 +
|-
 +
| 4
 +
| 0
 +
| 8
 +
| Random
 +
|-
 +
| 2
 +
| 0
 +
| 16
 +
| Random
 +
|-
 +
| 4
 +
| 8
 +
| 8
 +
| Random
 +
|-
 +
| 2
 +
| 16
 +
| 16
 +
| Random
 +
|}
 +
 
 +
'''Sessions 9-16'''
 +
Task: 6 switch, 3 size, 3 animacy, randomly (not counterbalanced)
 +
{| class="wikitable"
 +
! Quantity per session
 +
! Inter-item distractor time (s)
 +
! End of list distractor time (s)
 +
! Order in session
 +
|-
 +
| 2
 +
| 0
 +
| 0
 +
| Never list 1, otherwise random
 +
|-
 +
| 3
 +
| 0
 +
| 8
 +
| Random
 +
|-
 +
| 2
 +
| 0
 +
| 16
 +
| Random
 +
|-
 +
| 3
 +
| 8
 +
| 8
 +
| Random
 +
|-
 +
| 2
 +
| 16
 +
| 16
 +
| Random
 +
|}
 +
 
 +
==== Phase 3: Control for EFR -- identical to Phase 1 (EFR/TaskFR2)====
 +
 
 +
This Phase 3 differs from the original Phase 3 in that there is no externalized free recall. Participants are doing the exact same thing as in Phase 1 of the experiment.
 +
'''Sessions 17-20 '''
 +
{| class="wikitable"
 +
! Quantity per session
 +
! Task
 +
! Order in session
 +
|-
 +
| 4
 +
| NT
 +
| Random in lists 3-16
 +
|-
 +
| 4
 +
| Size
 +
| Random in lists 3-16
 +
|-
 +
| 4
 +
| Anim
 +
| Random in lists 3-16
 +
|-
 +
| 4
 +
| Switch
 +
| Lists 1-2. remainder random in 3-16
 +
|}
 +
 
 +
===Recognition===
 +
 
 +
This section tests the participant's recognition of words. During each trial, words are presented onscreen one at a time. For each word, participants are asked to report vocally whether or not they recognize the word from that day's session by saying "PESS" for YES and "PO" for No, and how confident they are in that response, using a scale of least confident (1) to most confident (5). Then, the participant receives immediate onscreen feedback about whether their response was correct or incorrect and how long it took them to respond. Some words in the list are targets, which are words that the participant saw in their word pool for that session.  Some words are lures, which are words that were not in their session that day. During the preliminary session, each participant trains the voice recognition software to their voice saying "PESS" and "PO". This allows accurate immediate feedback; the words YES and NO are much more difficult for the voice recognition software.
 +
 
 +
=== Additional experimental paradigm details ===
 +
==== Timing ====
 +
 
 +
Word presentation duration: 3000 ms
 +
 
 +
ISI: 800 ms with additional 400 ms jitter
 +
 
 +
Delay between end of study and recall: 1200 ms
 +
 
 +
Recall duration: 75 s
 +
 
 +
Constant rest before new list: 1500 ms
 +
 
 +
Delay before FFR begins: 5000 ms
 +
 
 +
FFR duration: 300 s
 +
 
 +
Recognition: ~25 minutes
 +
 
 +
Grey boxes in the figure above denote variable rest periods, the length of which is controlled by the participant.
 +
 
 +
== LtpFR2 (PEERS4) detailed methods ==
 +
This page delineates the structure of the ltpFR2 experiment. ltpFR2 is a 24 session experiment using scalp EEG technology. Initially, participants were screened for ltpFR2 using the [[ltpFR]] paradigm. Only those participants who had completed [[ltpFR]] could be recruited for ltpFR2. Completion of [[ltpFR]] served as a built-in screening process to determine participant reliability and desirability, and signified their prior completion of the behavioral studies (WAIS and WMS-CVLT). Presently, we screen participants for ltpFR2 using a preliminary session of pyFR. There is a free recall section of the ltpFR2 experiment, as well as distractor tasks between word lists.
 +
 
 +
See [https://upenn.app.box.com/file/462233347854 here] of a list of 98 subjects who completed all 24 sessions.
 +
 
 +
===Free Recall===
 +
 
 +
Throughout all sessions, participants view lists of words and recall them. Additionally, there is a distractor period where participants are asked to perform arithmetic equations (A+B+C). The distractor can take place during two times of the experiment: 1) before list 2) end-of-list. Both distractor periods are 24 seconds in duration. The before list distractor is presented 50% of the time, while the end-of-list distractor is always presented.
 +
 
 +
* For relevant documents regarding ltpFR2 testing and collection go to [https://memory.psych.upenn.edu/InternalWiki/Lab_Document_Organization here]
 +
 
 +
* Experiment code including word pools and WAS similarity matrix can be found in /home/svn/experiments/ltpFR2/trunk
 +
 
 +
* Data is located in /data/eeg/scalp/ltp/ltpFR2 and /protocols/ltp/subjects/<subject_code>/experiments/ltpFR2
 +
 
 +
* Behavioral data (presentation and recall events) for ltpFR2 can be publicly accessed [https://upenn.box.com/s/g5m8uqy2ozae5uwejg2pbbi36n3fbmaf here].
 +
 
 +
=== Methods ===
 +
[[File:ltpFR2_timeline.jpg|thumb|400px|ltpFR2 Timeline]]
 +
 
 +
====Summary====
 +
# 24 sessions
 +
#* 24 lists per session
 +
#* Sessions 1-23 use same 576 words for all participants
 +
#* Session 24 uses 288 old words and 288 novel (i.e. not used in sessions 1-23) words, and has three list types, evenly split:
 +
#** 8 lists composed of 8 old/16 new words
 +
#** 8 lists composed of 12 old/12 new words
 +
#** 8 lists composed of  16 old/8 new words
 +
# List Construction
 +
#* WAS semantic similarity scores were calculated for all possible word pairs in the full PEERS word pool of 1638 words
 +
#* Word pairs were divided into 4 linearly spaced semantic similarity bins (low, medium-low, medium-high, high similarity)
 +
#* 24 words per list
 +
#** 16 semantically controlled words
 +
#*** 2 pairs of words drawn from each similarity bin
 +
#*** 1 pair is presented contiguously, 1 pair is presented with at least 2 intervening items
 +
#** 8 random, unpaired words
 +
# Distractors:
 +
#* a) All A+B+C arithmetic
 +
#* b) Pre-list distractor: 24 seconds, present on ½ of lists
 +
#* c) Post-list distractor: 24 seconds, present on all lists
 +
# Stimulus duration + ISI w/ jitter
 +
#* 1600 ms stimulus duration
 +
#* 800-1200 ISI (800 fixed plus 0-400 jitter)
 +
 
 +
====Methods====
 +
 
 +
Participants performed a delayed free recall experiment consisting of 24 experimental sessions. Each session consisted of 24 trials, with each trial containing a list of 24 words, presented one at a time on a computer screen. A random half of the lists (excluding the first list) were preceded by a 24-second, distractor-filled delay, and all lists were followed by a 24-second distractor period. A free recall test followed the post-list distractor on each list. Lists 8 and 16 were followed by short breaks, during which experimenters entered the testing room to check on participants and adjust EEG electrodes as necessary.
 +
 
 +
Each trial began with a 10-second countdown, which was displayed onscreen. Participants were permitted to pause and resume this countdown at any time by pressing a key. After the countdown was complete, a fixation cross appeared on the screen for 1500 ms. For trials without a pre-list distractor, the fixation cross was immediately followed by the presentation of the first word. For trials with a pre-list distractor, this fixation cross was instead followed by a 24-second distractor period. After the distractor period, the screen went blank for a jittered 800--1200 ms (uniformly distributed), after which the first word was presented. Each word was presented on the screen in white text on a black background for 1600 ms, and was followed by a jittered inter-stimulus interval of 800--1200 ms (uniformly distributed). Following the inter-stimulus interval after the final word in each list, participants performed a distractor task for 24 seconds. This post-list distractor task was followed by a 1200--1400 ms (uniformly distributed) delay, after which a tone sounded and a row of asterisks appeared onscreen for 500 ms, indicating the start of the free recall period. Participants were given 75 seconds to recall aloud as many of the words from the current list as possible, in any order. A fixation cross was displayed onscreen for the duration of the recall period. Once 75 seconds had elapsed, the recall period ended and a blank screen was displayed for 1000 ms, after which the 10-second countdown for the next list began.
 +
 
 +
Both the pre-list and post-list distractor tasks consisted of answering math problems of the form A+B+C=?, where A, B, and C were positive, single-digit integers. Math problems were displayed onscreen one at a time in white text on a black background, and participants were instructed to type the answer to each equation as quickly and accurately as possible. New problems would continue to appear until the full 24 seconds had elapsed, at which point the final problem was immediately removed from the screen. Participants were given a monetary bonus based on the speed and accuracy of their responses.
 +
 
 +
Each session required 24*24=576 words. The word pool for this experiment consisted of a 576-word subset of the 1638-word pool used in ltpFR. This same 576-word pool was used to generate the lists for sessions 1 through 23. That is, participants saw the same 576 words in each of their first 23 sessions, but the ordering of these words was randomized for each session. The 24th session introduced a set of novel words, which were drawn from the remaining words in the larger 1638-word pool. Specifically, the 24th session included eight lists composed of 8 old words and 16 new words, eight lists composed of 12 old words and 12 new words, and eight lists composed of 16 old words and 8 new words. For all 24 sessions, lists were constructed such that varying degrees of semantic relatedness occurred at both adjacent and distant serial positions. Semantic relatedness between all words in the full word pool was determined using the Word Association Space (WAS) model described by SteyEtal04. WAS similarity values were used to group words into four similarity bins (high similarity: WAS score > 0.7; medium--high similarity: 0.4 < WAS score < 0.7; medium-low similarity: 0.14 < WAS score < 0.4; low similarity: WAS score < 0.14). Two pairs of words from each of the four bins were arranged such that the words of one pair occurred at adjacent serial positions and the words of the other pair were separated by at least two other items. These eight word pairs comprised 16 of the 24 words in each list. The remaining eight words in each list were selected and positioned at random.
 +
 
 +
== PEERS5 (VFFR) Detailed Methods ==
 +
This page outlines the structure and methodology of VFFR, a 10-session externalized free recall experiment. VFFR is also known as ltpFR2.5 or ltpFR2b (see prior FR studies [[ltpFR]] and [[ltpFR2]]).
 +
A number of participants who had completed ltpFR2 were recruited for VFFR.
 +
 
 +
 
 +
====Summary====
  
"EEG" stands for electroencephalogram. There are many different types of EEG nets, and you may have even worn one before. The EEG nets we use do not require gel or scalp abrasion. The electrodes are housed above a sponge, which sits on your scalp, that is soaked in an electrolyte solution to allow for good conductivity of your brain's electrical activity.  This solution is comprised of baby shampoo (to dissolve the oils on your scalp), de-ionized water, and potassium chloride. Although it is rare, some people do experience mild irritation form the solution.
+
#10 sessions
 +
#*1 practice block x 10 trials + 24 blocks x 24 trials per session
 +
#*Last 5 sessions: Externalized initial free recall period (10 minutes) prior to regular trials (recall instructions and bonus information initially given right before the 6th session begins)
 +
#*Each session uses the same 576 ltpFR2 wordpool in randomized order
 +
#Stimulus duration + ISI w/jitter
 +
#*1200-1800 ms stimulus duration
 +
#*1000-1600 ms jittered ISI
  
=== How to get involved ===
+
====Full Methods====
If you meet the following criteria:
+
Participants completed 10 experimental sessions. Each session consisted of 1 block of 10 practice trials, followed by 24 blocks of 24 trials each. Each block began with a 10-second countdown. After the countdown was complete, the first trial of the block began. On each trial, a black screen was shown for a jittered 1000-1600 ms (uniformly distributed), after which a single word appeared onscreen in white text for 1200-1800 ms (uniformly distributed). Following presentation, the screen went blank again and participants were instructed to pause briefly, and then vocalize the word they had just seen. If they began speaking within 1 second of the word leaving the screen, the message “Too fast.” appeared on the screen in red text. Participants were instructed to minimize the number of trials on which this occurred. After the participant finished speaking, a tone sounded, marking the end of the current trial. Speech was detected using a volume amplitude threshold. In addition to the 10-second countdown between blocks, two 2-minute mid-session breaks were administered after block 8 and block 16.
*
+
*
+
  
Contact us at memorylab@psych.upenn.edu or 215-746-0407.
+
In the last five sessions, the 1 practice block and 24 experimental blocks were preceded by a 10-minute initial externalized free recall period. Participants were instructed to recall as many words as possible from the previous sessions in any order, while also vocalizing any additional words that come to mind in their attempt to recall these items.

Latest revision as of 16:48, 7 June 2023

The Penn Electrophysiology of Encoding and Retrieval Study (PEERS) is a series of studies carried out between 2010 and 2020 to elucidate the EEG correlates of memory processes with a particular focus on retrieval dynamics in free recall. In conducting PEERS we set out to do an experiment in big science where many subjects (over 150 in PEERS1-3 and 98 in PEERS4) each contributed a large quantity of data (e.g., 6-8 sessions each in PEERS1-3, and 24 sessions in PEERS4) allowing for detailed analysis of individual subject behavior and physiology.

The PEERS dataset in its entirety (experiments 1-5) is available here on OpenNeuro in BIDS format (see instructions for downloading). This dataset is about 8.7 TB, which means it cannot fit on disk for most laptops, so it is recommended to work with partial downloads unless you have access to an HPC or a desktop with large disk space. We recommend using DataLad to manage downloading subsets of the data while retaining the full file tree - see this tutorial.

The BIDS format opens up access to a whole suite of open-source software tools for data processing and analysis. See a comprehensive list of software and integrations here. Of particular note are integrations with MNE-python and EEGLAB. BIDS Apps are a series of neuroimaging pipelines that work out of the box with BIDS-formatted data.

The PEERS1-3 behavioral dataset, in a lab-specific format with some additional fields generated during post-processing, can be downloaded directly here. As this dataset is substantially smaller, it may appeal to those not analyzing brain data.


PEERS publications

2022

  • Cohen, R. T. and Kahana, M. J. (2022). A memory based theory of emotional disorders. Psychological Review, 129(4), 742-776.
    (pdf, data)

  • Katerman, B. S., Li, Y., Pazdera, J. K., Keane, C., and Kahana, M. J. (2022). EEG biomarkers of free recall. NeuroImage, 246, 118748.
    (pdf, data, code)

2021

  • Aka, A., Phan, T. D., and Kahana, M. J. (2021). Predicting recall of words and lists. Journal of Experimental Psychology: Learning, Memory, and Cognition, 47(5), 765–784.
    (pdf)

  • Weidemann, C. T. and Kahana, M. J. (2021). Neural measures of subsequent memory reflect endogenous variability in cognitive function. Journal of Experimental Psychology: Learning, Memory, and Cognition, 47(4), 641–651.
    (pdf, code, Ephys data)

2020

  • Healey, M. K. and Kahana, M. J. (2020). Age-related differences in the temporal dynamics of spectra power during memory encoding. PLOSone, 15(1), e0227274.
    (pdf)

2019

  • Weidemann, C. T. and Kahana, M. J. (2019). Dynamics of brain activity reveal a unitary recognition signal. Journal of Experimental Psychology: Learning, Memory, and Cognition, 45(3), 440–451.
    (pdf, code, Ephys data)

2018

  • Kahana, M. J., Aggarwal, E. V., and Phan, T. D. (2018). The variability puzzle in human memory. Journal of Experimental Psychology: Learning, Memory, and Cognition, 44(12), 1857–1863.
    (pdf)

  • Kuhn, J. R., Lohnas, L. J., and Kahana, M. J. (2018). A spacing account of negative recency in final free recall. Journal of Experimental Psychology: Learning, Memory, and Cognition, 44(8), 1180–1185.
    (pdf)

2017

  • Long, N. M. and Kahana, M. J. (2017). Modulation of task demands suggests that semantic processing interferes with the formation of episodic associations. Journal of Experimental Psychology: Learning, Memory, and Cognition, 43(2), 167–176.
    (pdf)

2016

  • Healey, M. K. and Kahana, M. J. (2016). A four-component model of age-related memory change. Psychological Review, 123(1), 23–69.
    (pdf, supplemental, data, code)

  • Weidemann, C. T. and Kahana, M. J. (2016). Assessing recognition memory using confidence ratings and response times. Royal Society Open Science, 3, 150670.
    (pdf, code, Ephys data)

2015

  • Lohnas, L. J., Polyn, S. M., and Kahana, M. J. (2015). Expanding the scope of memory search: Modeling intralist and interlist effects in free recall. Psychological Review, 122(2), 337–363.
    (pdf, data, model, errata)

  • Long, N. M., Danoff, M. S., and Kahana, M. J. (2015). Recall dynamics reveal the retrieval of emotional context. Psychonomic Bulletin and Review, 22(5), 1328–1333.
    (pdf)

2014

  • Healey, M. K., Crutchley, P., and Kahana, M. J. (2014). Individual differences in memory search and their relation to intelligence. Journal of Experimental Psychology: General, 143(4), 1553–1569.
    (pdf, data)

  • Healey, M. K. and Kahana, M. J. (2014). Is memory search governed by universal principles or idiosyncratic strategies? Journal of Experimental Psychology: General, 143(2), 575–596.
    (pdf, data)

  • Lohnas, L. J. and Kahana, M. J. (2014). Compound cuing in free recall. Journal of Experimental Psychology: Learning, Memory and Cognition, 40(1), 12–24.
    (pdf, data)

  • Long, N. M., Burke, J. F., and Kahana, M. J. (2014). Subsequent memory effect in intracranial and scalp EEG. NeuroImage, 84, 488–494.
    (pdf, Ephys data)

2013

  • Lohnas, L. J. and Kahana, M. J. (2013). Parametric effects of word frequency in memory for mixed frequency lists. Journal of Experimental Psychology: Learning, Memory, and Cognition, 39(6), 1943–1946.
    (pdf)

2012

  • Miller, J. F., Weidemann, C. T., and Kahana, M. J. (2012). Recall termination in free recall. Memory & Cognition, 40, 540–550.
    (pdf)


PEERS 1-3 Detailed Methods

Introduction

This section provides a comprehensive overlook of the experimental methods for the PEERS (AKA ltpFR) experiment.

ltpFR is a 20 session experiment using scalp EEG technology, with 2 additional behavioral sessions (WAIS and WMS-CVLT). Participants are screened for ltpFR using the pyFR paradigm in a one session preliminary study. There is a free recall section of the experiment and a recognition section of the experiment. View a diagram of the session

For information about how to analyze the LTP data, please see the Scalp analysis page.

Each of the 20 sessions includes several different tasks: track ball, free recall, final free recall, recognition.

Trackball

Each session begins with the trackball task, which is intended to provide information on the EEG signals characteristic of different types of eye movements. Track ball proceeds as follows:

1. Asterisks are drawn at the center of the screen and at 12, 3, 6 and 9 o'clock positions.

2. The pre-recorded words "close" and "open" are played in sequence 5 times. The duration of the "close" and "open" clips are approximately 1480 and 1400 ms, respectively. Each word is followed by a delay interval of 5000 ms + uniformly distributed jitter drawn from the interval [0,300] ms.

3. The pre-recorded words "left" and "right" are played in sequence 5 times. The duration of the "left" and "right" clips are approximately 990 and 920 ms, respectively. Each word is followed by a delay interval of 2000 ms + uniformly distributed jitter drawn from the interval [0,300] ms.

4. The asterisks at the edge of the screen are hidden, and the asterisk at the center of the screen is caused to trace a curve defined by a B-spline fit to 10 randomly-selected screen coordinates. This is followed by a delay of 5000 ms + uniformly distributed jitter drawn from the interval [0,300] ms.

5. The asterisks described in 1. are displayed again.

6. The pre-recorded words "up" and "down" are played in sequence 5 times. The duration of the "up" and "down" clips are approximately 1060 and 1050 ms, respectively. This is followed by a delay of 5000 ms + uniformly distributed jitter drawn from the interval [0,300] ms.

7. Another curve-tracing stimulus is shown as in 4, followed by a delay with the same parameters.

8. The pre-recorded word "blink" is played 5 times. The duration of the clip is 695 ms, approximately. This is followed by a delay of 5000 ms + uniformly distributed jitter drawn from the interval [0,300] ms.

9. The close/open task described in 2. is repeated, with the same delay parameters.

Free Recall

Across all sessions, participants study lists of words and recall them. On a subset of lists, participants must perform a size or animacy judgment task. The task type is denoted by color, purple or green, font, and case (i.e, uppercase or lowercase) (assigned randomly for each participant). Participants must decide if the word presented is an object that is SMALL/BIG (can/cannot fit in a shoebox) or LIVING/NONLIVING. The participant is told in advance which color represents which judgment, and this assignment is consistent throughout all 20 of their sessions. For each word, they press one of four labeled buttons on the keyboard to make the appropriate judgment. There are no-task/control lists during which there is no judgment task, task-lists, during which participants perform either a size or animacy judgment on all list items, and switch-lists, during which participants alternate between size and animacy judgments within list.

The experiment has three phases, where different sessions had different manipulations, see below. The transition between phases changed after subject LTP209.

LTP063 to LTP209

Phase 1: Task Manipulation

Session 1 (practice)

Quantity per session Task Order in session
4 NT Lists 1-4
4 Size Either 5-8 or 9-12
4 Anim Either 5-8 or 9-12
4 Switch Lists 13-16

Sessions 2-7

Quantity per session Task Order in session
4 NT Random in lists 3-16
3 Size Random in lists 3-16
3 Anim Random in lists 3-16
6 Switch Lists 1-2. remainder random in 3-16

Phase 2: Distractor Manipulation

In Phase 2, arithmetic is introduced to the experiment in addition to everything the participant was performing in Phase 1. The arithmetic consists of adding three numbers 1 through 9, inclusive (A + B + C). It is ALWAYs three numbers and always addition. Participants are asked to answer as many math problems correctly as they can (i.e. they should balance speed and accuracy). There are 3 different math lists: inter-item distractor lists, in which the participant does a block of arithmetic before each word in the list; end-of-list distractors, in which the participant does a block of arithmetic after the list/right before the recall period; and no math lists. There is a counter on the top right of the screen, allowing the participant to see the number of correctly answered math problems throughout the session. The list number is reduced during this phase because the math adds additional time to the experiment. Take note: In this phase, there are no control (NT) lists, only 4 switching lists, and 8 single judgement lists (4 BIG/SMALL lists and 4 LIVING/NON-LIVING lists) for a total of 12 lists per session. Numbers in each cell of the table represent the number of seconds that each distractor type was presented.

Session 8 (practice) Task: 7 size lists, 7 animacy lists, randomly (not counterbalanced across distractor tasks)

Quantity per session Inter-item distractor time (s) End of list distractor time (s) Order in session
2 0 0 Never list 1, otherwise random
4 0 8 Random
2 0 16 Random
4 8 8 Random
2 16 16 Random

Sessions 9-14 Task: 6 switch, 3 size, 3 animacy, randomly (not counterbalanced)

Quantity per session Inter-item distractor time (s) End of list distractor time (s) Order in session
2 0 0 Never list 1, otherwise random
3 0 8 Random
2 0 16 Random
3 8 8 Random
2 16 16 Random

Phase 3: Externalized FR

In Phase 3, participants stop doing arithmetic and return to only doing the judgement task. In the original Phase 3, participants were asked to recall any words that are salient to them in addition to those that they remember seeing from the list. It is important to note that the participants are not doing a stream of consciousness recall in this task, but that they were instructed to recall only words that are particularly salient.

Sessions 15-20

Quantity per session Task Order in session
4 NT Random in lists 3-16
4 Size Random in lists 3-16
4 Anim Random in lists 3-16
4 Switch Lists 1-2. remainder random in 3-16

LTP210 to LTP293

Phase 1: Task Manipulation (taskFR)

Session 1 (practice)

Quantity per session Task Order in session
4 NT Lists 1-4
4 Size Either 5-8 or 9-12
4 Anim Either 5-8 or 9-12
4 Switch Lists 13-16

Sessions 2-7

Quantity per session Task Order in session
4 NT Random in lists 3-16
4 Size Random in lists 3-16
4 Anim Random in lists 3-16
4 Switch Lists 1-2. remainder random in 3-16

Phase 2: Distractor Manipulation (CDTFR)

Session 8 (practice) Task: 7 size lists, 7 animacy lists, randomly (not counterbalanced across distractor tasks)

Quantity per session Inter-item distractor time (s) End of list distractor time (s) Order in session
2 0 0 Never list 1, otherwise random
4 0 8 Random
2 0 16 Random
4 8 8 Random
2 16 16 Random

Sessions 9-16 Task: 6 switch, 3 size, 3 animacy, randomly (not counterbalanced)

Quantity per session Inter-item distractor time (s) End of list distractor time (s) Order in session
2 0 0 Never list 1, otherwise random
3 0 8 Random
2 0 16 Random
3 8 8 Random
2 16 16 Random

Phase 3: Control for EFR -- identical to Phase 1 (EFR/TaskFR2)

This Phase 3 differs from the original Phase 3 in that there is no externalized free recall. Participants are doing the exact same thing as in Phase 1 of the experiment. Sessions 17-20

Quantity per session Task Order in session
4 NT Random in lists 3-16
4 Size Random in lists 3-16
4 Anim Random in lists 3-16
4 Switch Lists 1-2. remainder random in 3-16

Recognition

This section tests the participant's recognition of words. During each trial, words are presented onscreen one at a time. For each word, participants are asked to report vocally whether or not they recognize the word from that day's session by saying "PESS" for YES and "PO" for No, and how confident they are in that response, using a scale of least confident (1) to most confident (5). Then, the participant receives immediate onscreen feedback about whether their response was correct or incorrect and how long it took them to respond. Some words in the list are targets, which are words that the participant saw in their word pool for that session. Some words are lures, which are words that were not in their session that day. During the preliminary session, each participant trains the voice recognition software to their voice saying "PESS" and "PO". This allows accurate immediate feedback; the words YES and NO are much more difficult for the voice recognition software.

Additional experimental paradigm details

Timing

Word presentation duration: 3000 ms

ISI: 800 ms with additional 400 ms jitter

Delay between end of study and recall: 1200 ms

Recall duration: 75 s

Constant rest before new list: 1500 ms

Delay before FFR begins: 5000 ms

FFR duration: 300 s

Recognition: ~25 minutes

Grey boxes in the figure above denote variable rest periods, the length of which is controlled by the participant.

LtpFR2 (PEERS4) detailed methods

This page delineates the structure of the ltpFR2 experiment. ltpFR2 is a 24 session experiment using scalp EEG technology. Initially, participants were screened for ltpFR2 using the ltpFR paradigm. Only those participants who had completed ltpFR could be recruited for ltpFR2. Completion of ltpFR served as a built-in screening process to determine participant reliability and desirability, and signified their prior completion of the behavioral studies (WAIS and WMS-CVLT). Presently, we screen participants for ltpFR2 using a preliminary session of pyFR. There is a free recall section of the ltpFR2 experiment, as well as distractor tasks between word lists.

See here of a list of 98 subjects who completed all 24 sessions.

Free Recall

Throughout all sessions, participants view lists of words and recall them. Additionally, there is a distractor period where participants are asked to perform arithmetic equations (A+B+C). The distractor can take place during two times of the experiment: 1) before list 2) end-of-list. Both distractor periods are 24 seconds in duration. The before list distractor is presented 50% of the time, while the end-of-list distractor is always presented.

  • For relevant documents regarding ltpFR2 testing and collection go to here
  • Experiment code including word pools and WAS similarity matrix can be found in /home/svn/experiments/ltpFR2/trunk
  • Data is located in /data/eeg/scalp/ltp/ltpFR2 and /protocols/ltp/subjects/<subject_code>/experiments/ltpFR2
  • Behavioral data (presentation and recall events) for ltpFR2 can be publicly accessed here.

Methods

ltpFR2 Timeline

Summary

  1. 24 sessions
    • 24 lists per session
    • Sessions 1-23 use same 576 words for all participants
    • Session 24 uses 288 old words and 288 novel (i.e. not used in sessions 1-23) words, and has three list types, evenly split:
      • 8 lists composed of 8 old/16 new words
      • 8 lists composed of 12 old/12 new words
      • 8 lists composed of 16 old/8 new words
  2. List Construction
    • WAS semantic similarity scores were calculated for all possible word pairs in the full PEERS word pool of 1638 words
    • Word pairs were divided into 4 linearly spaced semantic similarity bins (low, medium-low, medium-high, high similarity)
    • 24 words per list
      • 16 semantically controlled words
        • 2 pairs of words drawn from each similarity bin
        • 1 pair is presented contiguously, 1 pair is presented with at least 2 intervening items
      • 8 random, unpaired words
  3. Distractors:
    • a) All A+B+C arithmetic
    • b) Pre-list distractor: 24 seconds, present on ½ of lists
    • c) Post-list distractor: 24 seconds, present on all lists
  4. Stimulus duration + ISI w/ jitter
    • 1600 ms stimulus duration
    • 800-1200 ISI (800 fixed plus 0-400 jitter)

Methods

Participants performed a delayed free recall experiment consisting of 24 experimental sessions. Each session consisted of 24 trials, with each trial containing a list of 24 words, presented one at a time on a computer screen. A random half of the lists (excluding the first list) were preceded by a 24-second, distractor-filled delay, and all lists were followed by a 24-second distractor period. A free recall test followed the post-list distractor on each list. Lists 8 and 16 were followed by short breaks, during which experimenters entered the testing room to check on participants and adjust EEG electrodes as necessary.

Each trial began with a 10-second countdown, which was displayed onscreen. Participants were permitted to pause and resume this countdown at any time by pressing a key. After the countdown was complete, a fixation cross appeared on the screen for 1500 ms. For trials without a pre-list distractor, the fixation cross was immediately followed by the presentation of the first word. For trials with a pre-list distractor, this fixation cross was instead followed by a 24-second distractor period. After the distractor period, the screen went blank for a jittered 800--1200 ms (uniformly distributed), after which the first word was presented. Each word was presented on the screen in white text on a black background for 1600 ms, and was followed by a jittered inter-stimulus interval of 800--1200 ms (uniformly distributed). Following the inter-stimulus interval after the final word in each list, participants performed a distractor task for 24 seconds. This post-list distractor task was followed by a 1200--1400 ms (uniformly distributed) delay, after which a tone sounded and a row of asterisks appeared onscreen for 500 ms, indicating the start of the free recall period. Participants were given 75 seconds to recall aloud as many of the words from the current list as possible, in any order. A fixation cross was displayed onscreen for the duration of the recall period. Once 75 seconds had elapsed, the recall period ended and a blank screen was displayed for 1000 ms, after which the 10-second countdown for the next list began.

Both the pre-list and post-list distractor tasks consisted of answering math problems of the form A+B+C=?, where A, B, and C were positive, single-digit integers. Math problems were displayed onscreen one at a time in white text on a black background, and participants were instructed to type the answer to each equation as quickly and accurately as possible. New problems would continue to appear until the full 24 seconds had elapsed, at which point the final problem was immediately removed from the screen. Participants were given a monetary bonus based on the speed and accuracy of their responses.

Each session required 24*24=576 words. The word pool for this experiment consisted of a 576-word subset of the 1638-word pool used in ltpFR. This same 576-word pool was used to generate the lists for sessions 1 through 23. That is, participants saw the same 576 words in each of their first 23 sessions, but the ordering of these words was randomized for each session. The 24th session introduced a set of novel words, which were drawn from the remaining words in the larger 1638-word pool. Specifically, the 24th session included eight lists composed of 8 old words and 16 new words, eight lists composed of 12 old words and 12 new words, and eight lists composed of 16 old words and 8 new words. For all 24 sessions, lists were constructed such that varying degrees of semantic relatedness occurred at both adjacent and distant serial positions. Semantic relatedness between all words in the full word pool was determined using the Word Association Space (WAS) model described by SteyEtal04. WAS similarity values were used to group words into four similarity bins (high similarity: WAS score > 0.7; medium--high similarity: 0.4 < WAS score < 0.7; medium-low similarity: 0.14 < WAS score < 0.4; low similarity: WAS score < 0.14). Two pairs of words from each of the four bins were arranged such that the words of one pair occurred at adjacent serial positions and the words of the other pair were separated by at least two other items. These eight word pairs comprised 16 of the 24 words in each list. The remaining eight words in each list were selected and positioned at random.

PEERS5 (VFFR) Detailed Methods

This page outlines the structure and methodology of VFFR, a 10-session externalized free recall experiment. VFFR is also known as ltpFR2.5 or ltpFR2b (see prior FR studies ltpFR and ltpFR2). A number of participants who had completed ltpFR2 were recruited for VFFR.


Summary

  1. 10 sessions
    • 1 practice block x 10 trials + 24 blocks x 24 trials per session
    • Last 5 sessions: Externalized initial free recall period (10 minutes) prior to regular trials (recall instructions and bonus information initially given right before the 6th session begins)
    • Each session uses the same 576 ltpFR2 wordpool in randomized order
  2. Stimulus duration + ISI w/jitter
    • 1200-1800 ms stimulus duration
    • 1000-1600 ms jittered ISI

Full Methods

Participants completed 10 experimental sessions. Each session consisted of 1 block of 10 practice trials, followed by 24 blocks of 24 trials each. Each block began with a 10-second countdown. After the countdown was complete, the first trial of the block began. On each trial, a black screen was shown for a jittered 1000-1600 ms (uniformly distributed), after which a single word appeared onscreen in white text for 1200-1800 ms (uniformly distributed). Following presentation, the screen went blank again and participants were instructed to pause briefly, and then vocalize the word they had just seen. If they began speaking within 1 second of the word leaving the screen, the message “Too fast.” appeared on the screen in red text. Participants were instructed to minimize the number of trials on which this occurred. After the participant finished speaking, a tone sounded, marking the end of the current trial. Speech was detected using a volume amplitude threshold. In addition to the 10-second countdown between blocks, two 2-minute mid-session breaks were administered after block 8 and block 16.

In the last five sessions, the 1 practice block and 24 experimental blocks were preceded by a 10-minute initial externalized free recall period. Participants were instructed to recall as many words as possible from the previous sessions in any order, while also vocalizing any additional words that come to mind in their attempt to recall these items.