Opportunities for extra credit:
Keep checking at:
www.tatalab.ca
Upcoming
March 22
March 24
More about conscious
perception
Overview of Memory
Sensory Memory
March 29
March 31
Short-Term/Working
Memory (Brooks expt. 1)
Long-Term Memory
April 5
April 7
NO CLASS
Long-Term Memory and
False Memories (Loftus)
April 12
Consciousness and
“Perception without
Awareness”
April 14
Subliminal Messages (Vokey
and Read)
Memes (Dawkins)
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 forcedchoice 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 forcedchoice 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
“WHERE”
“WHAT”
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
RETRIEVAL
• Atkinson-Shiffrin Model
ATTENTION
Sensory
Signals
Sensory
Memory
Short-Term
Memory
Long-Term
Memory
REHEARSAL
“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 E
G S+ A U
T 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 B
O D+W A
I 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
# of letters
potentially
recalled
10
4
0
0 ms
500 ms
never
Probe Delay
Duration
• Partial Report
10
# of letters
potentially 4
recalled
0
0 ms
500 ms
Delay
never
Interpretation:
1. Information dwells in a brief storage “buffer”
2. duration of storage lasts about 1/2 of one second
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 capacity
3. pre-attentive