chapter 7: attention and scene perception

attention

any of the very large set of selective processes in the brain

• to deal with the impossibility of handling all inputs at once, the nervous system has evolved mechanisms that are able to restrict processing to a subset of things; places, ideas, or moment in time

How many types of attention?

7

• selective

• external

• internal

• overt

• covert

• divided

• sustained

selective attention

form of attention involved when processing is restricted to a subset of the possible stimuli

external

attending to stimuli in the worldi

internal

attending to one line of thought over another or selecting one response over another

overt attention

directing a sense organ toward a stimulis, like turning your eyes or your head

covert

attending without giving an outward sign you are doing so

divided

splitting attention between two different stimuli (no one is a good multitasker)

sustained (vigilance)

continuously monitoring some stimulus

inattentional blindness

a failure to notice—or at least to report a stimulus that would be easily reportable if it were attended

• what we see is often driven by our expectations of what we “should” be seeing"

change blindness

failure to notice change between two scenes

• if the change does not alter gist, meaning, of the scene, quite large changes can pass unnoticed.

  • demonstrates that we don’t encode and remember as much of the world as we might think we do

bottom-up processing

automatic, stimulus driven

top-down processing

controlled, goal driven

interaction

working together in complementary roles

reaction time

measure of the time from the onset of a stimulus to a response

cue

a stimulus might indicate where (or what) a subsequent stimulus will be

• cues can be valid ( correct info), invalid (incorrect), or neutral (uninformative)

Stimulus onset asynchrony

the time between the onset of one stimulus and the onset of another

Time Course of Attentional Cueing

Theories of Attention

Spotlight and Zoom Lens

Spotlight Model

attention is restricted in space and moves from one point to the next. areas within the spotlight receive extra processing

Zoom Lens Model

Attended region can grow or shrink depending on the size of the area to be processed

Visual Search

looking for a target in a display containing distracting elements

Guided search

attention is restricted to a subset of possible items based on ifnromation about the items basic feature (color or shape)

Target

goal of a visual search

Distractor

in visual search, any stimulus other than the target

Set size

number of items in a visual search display

Inhibition of return

relative difficulty in getting attention (or the eyes) to move back to a recently attended (or fixated) location

• during searches, IOR stops you from continually revisiting one spot

Efficiency of Visual Search

(measured by search slope, or ms/item) is the average increase in RT for each item added to the display

Feature Search

• efficient

  • search for a target defined by a single attribute, such as salient color or orientation

salience

vividness of a stimulus relative to its neighbors

parallel

in visual attention, referring to the processing of multiple stimuli at the same time

Conjunction search

search for a target defined by the presence of two or more attributes

• no single feature defines the target'

• defined by the co-occurrence` of two or more features

Scene-based guidance

information in our understanding of scenes that helps us find spceific objects in scenes

Binding problem

the challenge of tying different attributes of visual stimuli, which are handled by different brain circuits, to the appropriate object so we perceive a unified object

Feature Integration Theory (Anne Treisman)

limited set of basic features can be processed in parallel preattentively, but that other properties, including the correct binding features to objects, require attention

Preattentive stage

• process of a stimulus that occurs before selective attention is deployed to that stimulus

Illusory conjunction

an erroneous combination of two features in a visual scene

• provides evidence that some features are represeted independently and must be correctly bound together with attention

Rapid serial visual presentation (RSVP)

• experimental procedure in which stimuli appear in a stream at one location (typically the point of fixation) at a rapid rate (typically about 8 per second)

  • used to study the temporal dynamics of visual attention

Attentional Blink

difficulty in perceiving and responding to the sound of two target stimuli amid a RSVP stream of disteacting stimuli

Three ways responses of a cell could be changed by attention

• response enhancement

• sharper tuning

  • altered tuning

response enhancement

sharper tuning

altered tuning

Fusiform face area (FFA)

• an area in the fusiform gyrus of human extrastriate cortex that responds preferentially to faces, according to the fMRI studies

parahippocampal place area (PPA)

region of cortex in the temporal lobe of humans that appears to respond strongly to images of places (as opposed to isolated objects)

fusiform face area

parahippocampal place area

Visual-field defect

portion of the visual field with no vision or with abnormal vision, typically resulting from dsmage to the visual nervous system

• damage to the parietal lobe can cause a visual defect such that one side of the world is not attended to

Neglect

in visual attention, the inability to attend or respond to stimuli in the contralesional visual field

• typically, neglect of the left visual field after damage to the right parietal lobe

Nonselective pathway

contributes the information about the distribution of features across a scene as well as information about the gift of the scene. this pathaway does not pass through the bottleneck of attention

Selective pathway

permits the recognition of one or a very few objects at a time. this pathaway passes through the bottleneck of selective attention

Pathways to our perception of the world

Ensemble Statistics

average and distribution of properties, such as orientation or color, over a set of objects or a region in a scene

• nonselective pathway computes this

Spatial Layout

• description of the structure of a scene (enclosed, open, rough, smooth) without reference to the identity of specific objects in the scene