Opportunities for extra credit:

Keep checking at:www.tatalab.ca

March 22

More about conscious perceptionOverview of Memory

March 24

Sensory Memory

March 29

Short-Term/Working Memory (Brooks expt. 1)

March 31

Long-Term Memory

April 5

NO CLASS

April 7

Long-Term Memory and False Memories (Loftus)

April 12Consciousness and “Perception without Awareness”

Subliminal Messages (Vokey and Read)

April 14

Memes (Dawkins)

Upcoming

Perception and Cognition

• We have elaborate perceptual mechanisms to provide information to our brains to guide current or future behavior

Perception and Cognition

• We have elaborate perceptual mechanisms to provide information to our brains to guide current or future behavior

• Notice there’s no mention of consciousness

Perception and Cognition

• We have elaborate perceptual mechanisms to provide information to our brains to guide current or future behavior

• Notice there’s no mention of consciousness• Lot’s of information gets processed and

used by your brain without you noticing

Perception and Cognition

• We have elaborate perceptual mechanisms to provide information to our brains to guide current or future behavior

• Notice there’s no mention of consciousness• Lot’s of information gets processed and

used by your brain without you noticing• Consider an example

Blindsight and the Dorsal Stream• Lesions (usually due to stroke)

in primary visual cortex cause a region of blindness called a scotoma

• Identified using perimetry

X

Blindsight and the Dorsal Stream

• Patients with lesions to primary visual cortex occasionally retain some visual abilities:– better than chance performance on forced-

choice discrimination tasks– spatial navigation and coordination (i.e. avoid

obstacles, interact with environment)

Blindsight and the Dorsal Stream

• Patients with lesions to primary visual cortex occasionally retain some visual abilities:– better than chance performance on forced-

choice discrimination tasks– spatial navigation and coordination (i.e. avoid

obstacles, interact with environment)• Thought to be because of other “backdoor”

pathways that send signals to the Dorsal Stream, A.K.A the “Where and How Pathway”

Blindsight and the Dorsal Stream

• The Dorsal Stream is thought to mediate much spatial processing and interaction with the environment

“WHAT”

“WHERE”

Blindsight and the Dorsal Stream

• The Dorsal Stream is thought to mediate much spatial processing and interaction with the environment

• But the neural activity in these structures does not (is not alone sufficient to) enter into consciousness

The Hard Problem Returns

• MYSTERY: what is special about neural activity that leads to awareness ?

NOBODY KNOWS !

Attention and Consciousness

• Sensory information must be attended for it to be entered into awareness

• This involves a subtle interaction between perception and memory…

• Put another way: sensory information must be attended to be encoded into memory

Object Substitution Masking• Masking occurs when one stimulus impairs perception of a

nearby stimulus

• In special cases the stimuli don’t have to overlap in space or time!?

• Object Substitution masking occurs when attention cannot select a target object before it vanishes …AND…

• A mask is visible at the target location after the target has vanished

Object Substitution Masking• Masking highlights the complex and subtle interaction

between perception, attention, memory and awareness:

Shapes enter visual system

Mask cues attention to the target location

Conscious system tries to recover shape that had been there

Object Substitution Masking• Maybe we should learn more about memory…

MEMORY

Overview of Memory

• Atkinson-Shiffrin Model

Sensory Signals

Sensory Memory

Short-Term Memory

Long-Term Memory

ATTENTION

REHEARSAL

RETRIEVAL

“Types” of Memory

• Sensory Memory– brief ( < 1 second)– preattentive / parallel processing (very

large capacity)

Sensory Memory

Capacity

• Describe a simple experiment that could measure the capacity of “memory”

Capacity

• Describe a simple experiment that could measure the capacity of “memory”

• Briefly present some letters or digits and then ask the subject to report them– Called “whole report”

Capacity

+

Capacity

F S F EG S A UT O C G

+

Capacity

“Recall as many letters as you can”

Capacity

• George Sperling - Systematic investigation of memory capacity

– Result: subjects accurately recall 3 or 4 items

– What can you conclude from this result?

– Maybe subjects can only hold 3 or 4 items?

Capacity

• Could it be that subjects had encoded all the letters but failed to retrieve the information?

Capacity

• For example: What if they forgot the information before they could report it?– You would get the same result!

• How could you modify the experiment to measure the instantaneous capacity, before any forgetting can occur?

Capacity

• Partial Report - briefly present letters or digits and ask subject to report only some of them

“Report the letters in the row indicated by the arrow”

Capacity

+

Capacity

U E S BO D W AI B V S

+

Capacity

+

Capacity

+

Capacity

Which Letters?

Capacity

• Partial Report

• Result: subjects can recall any 3 or 4 letters that are indicated by the arrow !

Capacity

• Partial Report

• Result: subjects can recall any 3 or 4 letters that are indicated by the arrow !

• What does this mean about the capacity of memory?

Capacity

• There is some part of the perception system that stores huge amounts of information…

– in fact, if only a single letter is probed, instantaneous capacity is seen to be unlimited

Duration

• There is some part of the perception system that stores huge amounts of information…

• But for how long? How would you design an experiment to measure the duration of this high-capacity memory system?

Duration

• There is some part of the perception system that stores huge amounts of information…

• But for how long? How would you design an experiment to measure the duration of this high-capacity memory system?

• Vary the onset of the probe

Duration

• Partial Report

Probe Delay

# of letterspotentially recalled

500 ms0 ms never0

4

10

Duration

• Partial Report

Delay

# of letters potentiallyrecalled

Interpretation:1. Information dwells in a brief storage “buffer”2. duration of storage lasts about 1/2 of one second

500 ms0 ms never0

4

10

Iconic Memory

• a brief storage of “raw data” in the visual system

Echoic Memory

• Auditory information is stored in a similar sensory “buffer”– Echoic memory seems to last for several

seconds

Properties of Sensory Memory

1. Brief (iconic ~500ms; echoic ~2 seconds)

Properties of Sensory Memory

1. Brief (iconic ~500ms; echoic ~2 seconds)2. Virtually unlimited capacity

Properties of Sensory Memory

1. Brief (iconic ~500ms; echoic ~2 seconds)2. Virtually unlimited capacity3. pre-attentive