Lecture 7 – PSYB51
Attention and Scene Perception
What is the horopter?
> Entity of all the points and space, where for the two eyes there‘s zero disparity.
Selective attention is a cognitive brain mechanism that enables one to process relevant
inputs, thoughts, or actions while ignoring others that are less important, irrelevant or
Arousal: a global state of the brain reflecting an overall level of responsiveness.
> As your arousal increases, your attention decreases
Why we need attention.
• Bottlenecks: It is impossible to process everything at once. Lack of brain, lack of
Why can attention help us?
Where does attention play a role?
• Attention to vision
Attention to audition / touch / smell
• Attention across modalities
• Attention to thoughts
• Attention to motor tasks: ex. when you‘re doing something complex, it‘d change
your motor complex
Today: What effects does attention have?
• How can we study attention?
– Cues bias attention
– Visual search: ex. looking for waldo
– Attention in time: watching a movie
• The physiological correlates of attention: what changes in brain activity
• Scene perception
How can we measure attention?
• Reaction times: a measure of the time from the onset of a stimulus to a
response (ex. if you‘re waving a hand, how long does it take for him to see that)
• Perceptual thresholds: change with attention.
• Motor accuracy
• Brain activity
• Eye movements: can reflect overt shifts of attention. But careful; attention
can shift without eye movements: covert attention.
• Perceptual biases : somethings that are symmetrical are not perceived as
being symmetrical or vice versa How can we study attention?
– Cues bias attention
• Posner‘s attentional cueing paradigm (Michael Posner was the first person to develop
• Natural biases
• Feature-based cueing
– Visual search: where‘s waldo
– Attention in time
Simple probe detection experiment measures RT (or perceptual thresholds)
• Posner: adding a cue
• Cue: A stimulus that might indicate where (or what) a subsequent stimulus
will be: valid vs. invalid vs. neutral. => Cueing effect
> if it‘s on the left, in this case, it‘s valid because in the next step the target is there. But not
on the right side, so that‘s invalid.
Stimulus-driven cues: info conveyed through previous events at the same location.
• Voluntary cues:(spatial)info conveyed through cognitions & memory, often based
on language or other symbols-> usually an arrow pointing at a direction, but other
symbols also, L, R, etc.
What‘s the difference between stimulus-driven/ peripheral and voluntary/symbolic?
• Partially independent neural structures.
• Stimulus onset asynchrony(SOA): the time between the onset of one stimulus and the onset
– Different time courses of SOAs; slower effects for voluntary cues.
– Inhibition of return (IOR) …and something in between stimulus-driven and
Overt shifts of attention: A shift of attention accompanied by corresponding
movements of the eyes.
Covert shifts of attention: A shift of attention in the absence of corresponding
movements of the eyes
Perceptual biases: Asymmetries in perception between the left and right side of a
– Vary with task, e.g. listening to speech.
– When it comes to perception, we tend to focus more on the left visual field
Line bisection task
Grating scales: – Which bar has more of the thinner/thicker stripes?
> People prefer to choose the one that has thin stripes on the left
Grating scales: Electroencephalography: leftward bias associated w/ greater negativity
over the right brain >380ms.
Space-based cueing of attention
Feature based cueing of attention: attention is guided based on non-spatial
information about features.
– Cued feature becomes more ―visible‖ throughout the visual field = outside the focus of
Feature-based attention can be a disadvantage.
Zhang&Luck(2009):EEG response to occasionally flashed online). To probe the
selectivity of the visual system for the attended dots outside the focus of attention
Zhang&Luck(2009): EEG response to occasionally flashed dots outside the focus of
- feature-dependent modulation of the P1 suggest early influences feature-based attention
on extrastriate areas.
How can we study attention?
– Visual search
• Task and terms
• Feature searches
• Inefficient searches
• (Feature-)conjunction searches
• Models of visual search
Bunch of bars. Is there one that is unique?
Looking for a target in a display containing distracting elements
• Target: the goal of visual search
• Distractor: any stimulus other than the target
• Set Size: the number of items in a visual display (for eg. In one set there
were more squares)
– Has no influence on search time for ―efficient searches‖, because it pops out
– Impacts search time for ―inefficient searches” : the time it takes you to find the object takes long
How much time