PSY 368 Human Memory

Sensory Memory

Structural Model

• Memory composed of storage structures that hold memories for a period of time • Sensory memory• Short-term memory (STM)• Long-term memory (LTM)

Sensory Memory• Sensory memory

• Very short storage of info from senses • Functions:

• To allow further processing of the info (STM)• Helps us to connect our sensory experiences

• Multiple stores:• Visual sensory memory = iconic memory (Neisser, 1967)• Auditory sensory memory = echoic memory• Touch sensory memory = haptic memory

The eye and how it behaves

• At its center is the fovea, a pit that is most sensitive to light and is responsible for our sharp central vision.

• The central retina is cone-dominated and the peripheral retina is rod-dominated.

• Limitations of the visual field• 130 degrees vertically, 180

degrees horizontally (including peripheral vision)

• Eye Movements serve two major functions• Saccades to Fixations – Position target objects of

interest on the fovea• Duration 10ms - 120ms• Very fast (up to 700 degrees/second) • No visual perception during saccades

• Tracking – Keep fixated objects on the fovea despite movements of the object or head

• eye movement video

• Eye Fixations perceptions are gathered during fixations• 90% of the time the eye is fixated• duration: 150ms - 600ms

Video examples: 1 | 2 | 3 | 4

The eye and how it behaves

• Questions:• What happens to the visual

image?• How do we get information out

of the image?• How do we connect visual

images (from different fixations)?

• One answer: have a memory storage separate from the visual image itself

Iconic Memory

Video example

Iconic Memory• Is there scientific evidence for iconic

memory?• The number of items that can be accurately

perceived at a glance• The number of objects that can be attended to at

once

• Problem: If the info decays quickly, subjects don’t have enough time to report it.

Iconic Sensory Storeyour iconic memory does this…

…but faster!

If I show you this….

• Reports of “seeing” a scene after it disappeared• This introspective description was suggestive of

some kind of "single, visible, precategorical, high-capacity, quickly-decaying memory that holds incoming visual stimulation for further processing" (Loftus & Irwin, 1998).

Iconic MemoryGeorge Sperling (1960)•Believed that he can see more than he can report

• The limitation is not in storing the information but in reporting it

• Solved this problem (span limit problem) and supported the existence of iconic memory

• Used two techniques:• whole report• partial report

50 msec

Report Cue

Iconic Memory

Whole Report:•Presented a 4 x 3 matrix of letters and digits for 50 ms, and asked subjects to report all the items they saw.

ready

+

A N P L

K M D T

W B S R

Iconic MemoryWhole Report:•Subjects are shown an array of items and asked to report all the items they saw.

A N P L

K M D T

W B S Rso 9/12 would be = 75% accuracy

Results: •Subjects could not report more than about 4.5 items on each trial. (4.5/12 = 38%)

•held true over wide range of exposure durations (.015 - .5 sec)

50 msec

Report Cue

Iconic Memory

Partial Report:•4 x 3 matrix of letters for 50 ms, subjects report all the items from one particular row.

• He cued them which row to report by playing a high, medium, or low tone.

(I have horn, drum, pong)

S B U C

M Y D F

L K W D

S B U C

M Y D F

L K W D

S B U C

M Y D F

L K W D

ready

+

B M C K

N V P A

W J U L

Iconic MemoryPartial Report:•Subjects are shown an array of items and asked to report a subset of the items they saw.

B M C K

N V P A

W J U LSo 3/4 = 75% accuracy

Results: •Subjects could typically report all 4 items on each trial. (4/4= 100%)

Iconic Memory• So far we’ve addressed capacity of iconic memory,

what about duration, how long does it last?• Effect of delay of tone

Report Cue• Varied time between the disappearance of the display and the onset of the cue tone: 0 to 1 sec

Iconic MemoryResults:•With short delays, can report proportionately more, but with longer delays partial report performance is similar to whole report

Report Cue

Iconic Memory

• Conclusions from Sperling (1960):• Evidence of iconic memory• Properties:

• High capacity of information• Very short duration (lasts about.5 sec)• Pre-categoical (“raw,” unprocessed) information

(we’ll return to this)

Iconic Memory

• Memory vs. afterimage of the eye?

A little on color vision• Trichromatic theory

of color vision“Blue”

“Green”

“Red”

Blue

WavelengthInput

Cones Signal to Brain

Yellow

Equal Parts Red and Green =

A little on color vision• Trichromatic theory

of color vision• Opponent Process

Theory• Red opposes Green• (Red + Green) opposes Blue

• Explains color afterimages

Iconic MemoryBanks and Barber

(1977) • Similar to Sperling

methodology• If using a retinal after-

image then letters with complimentary colours would be reported• Red becomes Green• Yellow becomes Blue

K J FS B NE W P red

50 msecpresentation

shortinterval

(250 msec)

report cue

Results:- their data showed subjects

can recall correctly with a color cue

Iconic Memory• Is the information in iconic memory

“unprocessed?”• Pre-categorical report: based on sensory

properties (location/color)• Post-categorical report: based on

categorical properties (type of item - letters or digits)• Von Wright (1972)• Merikle (1980)

Iconic Memory

Von Wright (1972)Used partial report

method with different report criteria• type (numbers vs

letters)• color• location

Is info in iconic memory pre-categorical?

Iconic Memory• BUT Merikle (1980) used

different kinds of displays (perceptual groupings, letters, and numbers) and found that the partial report advantage for type (number vs letter) as strong as location

• So it’s possible info processed to some degree

Problems with Iconic Memory

1. Information may not be precategorical• e.g., Merikle (1980)

2. The idea of output interference rather than decay.• Dick (1971) found that the first item was reported correctly

equally often for whole and partial reports.• The act of recalling one item can interfere with recall of the next item, so the more

items you're required to report, the less likely you are to report the last one successfully

3. The types of errors that the subjects make.• Auditory confusion errors (e.g. if letter is B, subjects more likely to

report V than R)• Mewhort & Leppman (1985) – identification (‘T’ was there or not)

error rates didn’t increase with duration between display and probe

Sensory Memory4. An important distinction:

• Stimulus persistence: Something that looks or sounds like the stimulus continues to be present for a short amount of time after the stimulus is no longer present

• Information persistence: Information can be extracted from a stimulus for a short amount of time after the stimulus is no longer present

Early view: stimulus persistence and information persistence were basically the same thing.

But more recent research suggests that:• Stimulus persistence reflects residual neural activity after exposure to a

stimulus• Information persistence reflects the same type of memory that is used for

longer-lasting information

Echoic Memory• Sensory memory for auditory

information• Not as much research done on echoic

memory as iconic

The ear and how it behaves

Changes in Air Pressure

• Stimulus is much more linear and transitory

Echoic Memory• Darwin, Turvey, and Crowder (1972)

• Whole report: report all 3 lists• For partial report, the cue was: - light on the left = report left

speaker list - light on the right = report right

speaker list - light in the center = report list

that was • The interval from list offset to

cue onset was: - 0 seconds, 1 second, or 4

seconds

Echoic Memory

• Findings:• Partial report

advantage up until about 4 sec • so echoic memory lasts 4

s or more• Echoic memory holds

less than iconic memory

• Darwin, Turvey, and Crowder (1972)

Echoic Memory• Some of the Effects discovered in

study of echoic memory• Using Immediate Serial Recall tasks

• Presented a list of items and asked to recall them in the order in which they were presented• Recency effect• Modality effect• Suffix effect

• Note: while these effects were discovered in the study of echoic memory, they are currently believed to reflect general memory principles rather than exclusively features of echoic memory

Echoic Memory

• Recency effect - last item of list better remembered than items earlier in the list

Echoic Memory

• Suffix effect - recency effect disappears if an auditory item follows last list itemTypical Suffix Effect experiment

has 2 conditions:• Control condition list of auditory items presented.• Suffix condition the same, except that each list is followed by a spoken word.

• Why the effect?• Interference from last item

disrupts memory trace

Echoic Memory• Modality effect - last item of list better remembered

when presented aloud than visually or silently

Why? Acoustic information persistence lasts approx. 2 seconds -- unless a subsequent similar stimulus interferes with it.When the subject reports the last item, it is still present in echoic memory.In contrast, visual stimulus persistence doesn't last that long.

Sensory Memory Summary

(1)Capacity - limited only by amount of info that can be received by the perceptual system (e.g., eye, ear)

(2) Duration of memory:- iconic - up to about 1 sec- echoic - about 4 - 20 sec depending on type of info

(3) Type of info - mostly pre-processed, but some processing may occur after 250 - 300 ms