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Summaries of lectures 9 to 16 from Perception to Consciousness
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detailed summaries of lectures 9 to 16 for the course from Perception to Consciousness by Victor Lamme
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Lecture notes part 2Lecture 9: Attention
Change blindness (video of murder mystery)
What is attention for?
- Primary task: which sensory inputs are selected for action?
- Dichotic listening task: shows selective attention; only able to attend to one stream
of auditory input at a time. There is thus limited capacity for perception to action!
- Attention in the visual domain:
o Overt attention: moving eyes, head, body, etc. in direction of relevant
stimulus (with superior colliculus)
o Covert attention: focus on stimulus, but actual attention is on different part
of the visual field. (moving the “inner eyes”)
- Covert attention in auditory domain: Cocktail Party Effect
o You can listen to something/someone else while seeming to listen to the
person in front of you
o Attentional Capture also part of this: sudden capture of auditory attention
(due to hearing your name, etc.) during a conversation
Top-Down Attention
- Attention with intention
- Posner Cueing Task: instruction to focus attention to certain location of the visual
field by means of an arrow; “invalid trials” (incongruent with target) are slower
reaction times than “valid trials” (congruent with target)
Bottom-Up Attention
- Automatic capture of attention
- Sudden appearance of a stimulus, even when told to ignore it, captures attention
and leads to shorter reaction time for valid primes compared to invalid primes
- Only works if within 100ms, if >300ms: “inhibition of return”; active suppression of
focus on the appeared stimulus leads to the opposite effect -> reaction time in the
valid primes is actually longer
These were all spatial attention
examples
Object Based Attention: when
perceived as an object, cueing
of a part of that object, leads to
faster detection of another part
of that object, even when
another object is separating
those parts of the object.
,Another Object Based Attention experiment:
- Two white lines; can be perceived as holes or objects. A target que is shown, which
could be at the correct location (valid), the wrong location but same line (invalid,
within), or on the wrong location and wrong line (invalid, between).
- If perceived as HOLES: no difference between invalid – within and invalid – between
- If perceived as OBJECTS: invalid – within is faster response time than invalid –
between
- There is thus object-based attention, and it drives us to focus on the boundaries
within the object when given a cue on it
Feature Based Attention
- “what object is different from all the other objects?”
- This is easier (and faster) when you are given a clue on what feature (color, shape,
etc.) to attend to
What is the effect of attention on visual system processing?
- Simply a larger response if attention is focused at the stimulus location
- This is in Top-Down attention shown with the Posner cueing task
- Shown in P1 component when recorded from the scalp (EEG)
- This is specific for the attended location; enhanced response is visible in the visual
cortex region associated with where the stimulus is shown
o This is also evident for attentional capture (bottom up). And inhibition of
return; in which the cue location shows a decreased response, in accordance
with decreased attention at that site
Attention on specific neurons (in monkeys):
- Neuron in V4 with preference to a vertical blue rectangle (vs a white horizontal one)
o Shows higher response when attended to the vertical blue rectangle than to
the white horizontal one
- Attention to specific features: (neural correlates of feature-based attention)
o Attention to a specific feature (direction of motion in this case) enhances
responses to that feature all over the visual field; increased signals of
attended features
o Shown in that when the focus of the monkey is on “upward movement”, the
response in a different area (MT) with preference for upward motion is
stronger than when attending to “downward movement”
o This shows again “positive attentional modulation”
- Also works for color (V4)
o A dot indicates the color that needs to be attended to
o Response to preferred (on fixation point) and non-preferred (outside fixation
point) both show larger response when its feature is attended to (black or
white)
- And Object Based Attention
o Increased signals of attended object; in FFA vs PPA
o Attending to face enhances activity in FFA
o Attending to houses enhances activity in PPA
,Increased Synchrony
- In monkey area V4: attention increases synchrony between two neurons that
process the attended stimulus
Feature vs Conjunction target search
- Feature search: searching for one feature (red or triangle or number or letter, etc.).
Targets will “pop out”; no increase of reaction time when display size increases
- Conjunction search: searching for multiple features in one target (red + triangle,
etc.). The larger the display size, the longer the reaction time
- Why? -> conjunction of features requires the binding of features, binding can only be
performed when looking at one or a few items at the same time, hence the increase
in reaction time with display size. Conjunction can thus only be done in a “serial”
way.
o Feature Integration Theory (FIT): features are detected parallel across the
visual field (color and shape simultaneously). But when attended to a specific
location, these features are integrated. The attentional capacity limit only
allows us to be able to integrate features at one or a few at a time
o FIT has clear similarity with Assembly Coding: both propose some sort of
mechanism to integrate features for object representation. In FIT, the “glue”
that forms the assembly is attention
Why does enhanced synchrony (sensory activity) actually lead to faster response times?
Stronger responses reach the threshold earlier for initiating a movement
Biased Competition Theory
- Crowding: inability to identify objects in peripheral vision when surrounded by other
objects, why?
o Small receptive fields (in fovea) can find the target object even when
surrounded by other objects. But in the periphery, receptive fields are larger,
making it very hard to discern the target from the surround; the field is
“polluted”.
o If the objects in the periphery are further away from the target, also the
larger receptive fields can identify the target
- Crowding at the neural level:
o Attention serves for filtering away unwanted information, so that attended
information can be processed properly
o When a preferred and non-preferred (poor) stimulus is shown, the firing rate
for that neuron diminishes when the non-preferred stimulus is increasingly
more visible next to the preferred stimulus
- Biased Competition:
o When two stimuli are shown together (face + house), there is competition; a
face selective cell will show a weaker response when the house is also in that
visual field
o But attention can bias this competition; increased response when the
attention is focused on either only the face or the house, allowing for a
response as when only a single stimulus was shown
o “attention resolves the competition”
, fMRI study on attention and resolution: (showing biased competition)
- (1) Sequential condition: in large receptive field (V4), every 250ms one stimulus is
shown in a specific corner of that field. The combined activation is the sum of the
four stimuli.
- (2) Simultaneous condition: in same large receptive field (V4), only in the first 250ms
all four stimuli are shown. The combined activation is the average of all the four
stimuli.
- BUT! when asked to focus attention on one specific stimulus in both conditions, the
combined activation is the same for both conditions; only the activation of that one
stimulus is reflected in the response. Attention thus biases the competition within
that receptive field, which leaves the combined activation in V4 to a similar response
as is seen in V1 (like a smaller receptive field).
- Attention thus increases the resolution of high-level cells!
What happens to unattended stimuli?
- Change blindness: the inability to notice changes that would be easily noticeable if
attention is directed at it
o Blank interval is important for blindness to occur
o “mud-splashes” also work as diversion
o Slow change blindness also works
- Unattended stimuli are clearly not available at the output/memory level, but where
in the process is it “deleted”?
o Early vs late processing
o V4 neurons: attention effect that increases firing is present exactly when a
response starts. Even the baseline is higher for attended neurons (they are
“warmed up”)
o At what level of processing does attention arise?
Not only in higher visual areas
Just depends on the type of stimuli used
Not only in ventral streams; both ventral and dorsal have attentional
effect
- Inattentional Blindness: the inability to memorize and report salient stimuli when
attention is directed at some other task-relevant stimulus. (like the gorilla video)
Lecture 10: Attention
Inattentional blindness paradigm:
- Task 1: Focus on words and remember them; accuracy 70%
- Task 2: Focus on pictures, surprise of being asked about the words; accuracy same as
if words were “recalled” that were never shown (foils)
o Unattended words are not distinguished from non-words
o Left frontal and temporal cortex both show processing when attended to the
words, and both no processing when not attended to the words (attending
the pictures); support for Early Processing!
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