forgetting and interference in short-term memory brown-peterson task proactive interference (pi)...

Forgetting and Interference in Short-term memory  Brown-Peterson Task

Proactive Interference (PI)Release from PI

Retrieval of info from STMSternberg (1966)

TaskStagesFindings

Forgetting and Interference in Short-term memory 

Brown (1959) Peterson and Peterson (1959) both tested a decay theory of immediate memory considered possibility of proactive interference

Task (Brown-Peterson task)

Brown-Peterson task

get 3 letters to remember

get a number (start counting backward by 3s)

recall letters when given a cue

+ + +

X S V

3 6 1

*****

+ + +

D L F

2 9 2

*****

P(r)

1.0

0.0

Proportion of Items Recalled as a Function of(Filled) Retention Interval

Retention Interval (s)

0 3 6 9 12 15 18

P(r)

1.0

0.0

Proportion of Items Recalled as a Function of(Filled) Retention Interval

Retention Interval (s)

0 3 6 9 12 15 18

P(r)

1.0

0.0

Proportion of Items Recalled as a Function of(Filled) Retention Interval

Retention Interval (s)

0 3 6 9 12 15 18

Decay orProactiveInterference?

Considered Proactive InterferenceLooked at performance for 4 blocks of trials

If PI occurred, then performance should getworse across the 4 blocks of trials

Considered Proactive InterferenceLooked at performance for 4 blocks of trials

If PI occurred, then performance should getworse across the 4 blocks of trials

Mean % Accuracy by Block

Block1 2 3 4

33 41 40 43

Considered Proactive InterferenceLooked at performance for 4 blocks of trials

If PI occurred, then performance should getworse across the 4 blocks of trials

Mean % Accuracy by Block

Block1 2 3 4

33 41 40 43

No evidence of PI; so, seems like evidence for decay(also thought retroactive interference was eliminated)

Peterson and Peterson (1959) used 2 practice trials then looked at mean performance for blocks of 12 trials

Keppel and Underwood (1968) Maybe PI builds up quickly examined performance over first few trials

If PI occurs, then performance should get worseacross trials (the more trials, the more PI)

P(r)

1.0

0.0

Proportion of Items Recalled by Trial NumberAnd Recall Delay

Trial Number

1 2 3 4 5 6

3-s delay

18-s delay

Keppel and Underwood (1968) Maybe PI builds up quickly examined performance over first few trials

If PI occurs, then performance should get worseacross trials (the more trials, the more PI)

Conclusion: PI occurs, builds up quickly

P(r)

1.0

0.0

Proportion of Items Recalled by Trial NumberAnd Recall Delay

Trial Number

1 2 3 4 5 6

3-s delay

18-s delay

Keppel and Underwood (1968) Maybe PI builds up quickly examined performance over first few trials

If PI occurs, then performance should get worseacross trials (the more trials, the more PI)

Conclusion: PI occurs, builds up quicklyAlso, little forgetting without PI(evidence against decay theory)

Keppel and Underwood (1968) Maybe PI builds up quickly examined performance over first few trials

If PI occurs, then performance should get worseacross trials (the more trials, the more PI)

Conclusion: PI occurs, builds up quicklyAlso, little forgetting without PI(evidence against decay theory)

Note: distractor task is producingretroactive interference, too

Wickens (1968) obtained quick build-up of PI with different

category exemplars (e.g., examples of professions,fruits, etc.)

Manipulation – category switch continued with same category (no switch) vs.

changed to a new category (switch)

P(r)

1.0

0.0

Proportion of Items Recalled by Trial NumberAnd Recall Delay

Trial Number

1 2 3 4 5 6

professions

fruits fruit(no switch)

fruit(switch)

Wickens (1968) obtained quick build-up of PI with different

category exemplars (e.g., examples of professions,fruits, etc.)

Manipulation – category switch continued with same category (no switch) vs.

changed to a new category (switch)

Release from PI due to a shift in materialConclusion: Build-up of PI due to similar material

(interference from similar material)

Forgetting and Interference in Short-term memory  Brown-Peterson Task

Proactive Interference (PI)Release from PI

Retrieval of info from STMSternberg (1966)

TaskStagesFindings

Retrieval of info from STM Sternberg’s (1966) task first, get a set of letters to remember (B K V J)

called the memory set(the memory set size can vary)

Retrieval of info from STM Sternberg’s (1966) task first, get a set of letters to remember (B K V J)

called the memory set(the memory set size can vary)

then get a probe (a letter): encode the probe

Retrieval of info from STM Sternberg’s (1966) task first, get a set of letters to remember (B K V J)

called the memory set(the memory set size can vary)

then get a probe (a letter): encode the probe scan items in STM

Retrieval of info from STM Sternberg’s (1966) task first, get a set of letters to remember (B K V J)

called the memory set(the memory set size can vary)

then get a probe (a letter): encode the probe scan items in STM make decision: Is the probe a letter in the memory set ?

Retrieval of info from STM Sternberg’s (1966) task first, get a set of letters to remember (B K V J)

called the memory set(the memory set size can vary)

then get a probe (a letter): encode the probe scan items in STM make decision: Is the probe a letter in the memory set ? press button for yes (a positive response)

or button for no (a negative response)

Retrieval of info from STM Sternberg’s (1966) task first, get a set of letters to remember (B K V J)

called the memory set(the memory set size can vary)

then get a probe (a letter): encode the probe scan items in STM make decision: Is the probe a letter in the memory set ? press button for yes (a positive response)

or button for no (a negative response)

Collect reaction time (RT) for response

B V

V

R C

T

B V M S

S

R C G W

T

Encode probe

Scan:Compare probe to items in memory set

Decisionyes/no

Execute motor response

Encode probe

Scan:Compare probe to items in memory set

Decisionyes/no

Execute motor response

How do we scan items in STM?

Encode probe

Scan:Compare probe to items in memory set

Decisionyes/no

Execute motor response

How do we scan items in STM?

all at the same time (parallel search)?one at a time (serial search)?

RT(ms)

Reaction Time as of Memory Set Size

Memory Set Size

1 2 3 4 5 60

400

500

600

700

RT(ms)

Reaction Time as of Memory Set Size

Memory Set Size

1 2 3 4 5 60

400

500

600

700

Scan all items at once(parallel search)

RT(ms)

Reaction Time as of Memory Set Size

Memory Set Size

1 2 3 4 5 60

400

500

600

700

Scan items one at a time(serial search)

RT(ms)

Reaction Time as Function of Memory Set Size

Memory Set Size

1 2 3 4 5 60

400

500

600

700

RT(ms)

Reaction Time as Function of Memory Set Size

Memory Set Size

1 2 3 4 5 60

400

500

600

700

Scan items one at a time(serial search)!

RT(ms)

Reaction Time as Function of Memory Set Size

Memory Set Size

1 2 3 4 5 60

400

500

600

700

RT = mx + b

RT(ms)

Reaction Time as Function of Memory Set Size

Memory Set Size

1 2 3 4 5 60

400

500

600

700

RT = mx + b

m, slope of linex, # of items in mem setb, y-intercept

RT(ms)

Reaction Time as Function of Memory Set Size

Memory Set Size

1 2 3 4 5 60

400

500

600

700

RT = mx + b

m = 38 ms (slope)x, # of items in mem setb = 397 ms (y-intercept)

RT(ms)

Reaction Time as Function of Memory Set Size

Memory Set Size

1 2 3 4 5 60

400

500

600

700

RT = 38x + 397

m = 38 ms (slope)x, # of items in mem setb = 397 ms (y-intercept)

Encode probe

Scan:Compare probe to items in memory set

Decisionyes/no

Execute motor response

Encode probe

Scan:Compare probe to items in memory set

Decisionyes/no

Execute motor response

Slope38 ms peritem in set

y-intercept y-intercept

Serial search

Question: Exhaustive or Self-terminating Search?

Exhaustive: Scan all the items in the memory set(no matter what)

Self-terminating: Stop scanning if a match is found

Serial search

Question: Exhaustive or Self-terminating Search?

Exhaustive: Scan all the items in the memory set(no matter what)

Self-terminating: Stop scanning if a match is found “no” vs. “yes” responses

“no” responses: must scan all items (to know probe is not in the set)

“yes” responses: could scan all items OR stop scanning if match found

Serial search -- “no” vs. “yes” responses“no” responses: must scan all items

(to know probe is not in the set)

“yes” responses: could scan all items OR stop scanning if match found

ReasoningIf the scanning is exhaustive (regardless of whether

the probe is present in the memory set) then the slopes of RT functions should be the same for “yes” and “no” responses.

If the scanning is self-terminating, then the slope of the “yes” RT function should be half that of the “no” RT function. Why? On average, the probe will occur half-way through the serial scanning.

RT(ms)

Reaction Time as Function of Memory Set Size

Memory Set Size

1 2 3 4 5 60

400

500

600

700Exhaustive searchprediction “No”

“Yes”

RT(ms)

Reaction Time as Function of Memory Set Size

Memory Set Size

1 2 3 4 5 60

400

500

600

700Self-terminating search prediction

“No”

“Yes”

RT(ms)

Reaction Time as Function of Memory Set Size

Memory Set Size

1 2 3 4 5 60

400

500

600

700Actual finding

“No”

“Yes”

Serial search

Question: Exhaustive or Self-terminating Search?

Exhaustive: Scan all the items in the memory set(no matter what)

Self-terminating: Stop scanning if a match is found

Serial search

Question: Exhaustive or Self-terminating Search?

Exhaustive: Scan all the items in the memory set(no matter what)

Seems kind of weird. Why not stop if there is a match?

Serial search Question: Exhaustive or Self-terminating Search?

Exhaustive: Scan all the items in the memory set(no matter what)

Seems kind of weird. Why not stop if there is a match?

Don’t confuse scanning stage with the decision stage.

If scanning is fast but decision is slow, then it is more efficient to scan all items, then make a single decision compared to making a decision after scanning each item (i.e., making multiple decisions).

Forgetting and Interference in Short-term memory  Brown-Peterson Task

Proactive Interference (PI)Release from PI

Retrieval of info from STMSternberg (1966)

TaskStagesFindings