Visual Attention

Change Blindness

Our inability to notice changes to a visual scene - change needs to occur when attention is not drawn to location of change but change must be obvious when attention is drawn to it

Attention

The ability to preferentially process some parts of a stimulus at the expense of processing of other parts of the stimulus. - needed as perceptual system has limited capacity. System would become overwhelmed if tried to process everything in a scene = attention helps avoid becoming overwhelmed

Overt Attention

Involves looking directly at an object.

Covert Attention

Involves looking at one object but attending to another object. e.g. looking at a book while being aware of people talking nearby.

Saccades

The eye movements between fixations that are ballistic (i.e. very fast) - when eyes jump from point to point. rests between jumps where eyes stay looking directly at a part of scene= fixation

Salience

The quality of being particularly noticeable or important - contrast

• colour/luminance

• size

• orientation

• motion/flicker

Attentional Capture

An initial process where fixations are captured by salient parts of a scene.

Effects of Attention

Attention speeds responses, influences appearance and affects the physiological response to a stimulus.

Binding Problem

The issue of how an object’s individual features are combined to create a coherent percept. Becomes more difficult when there are multiple objects

Illusory Conjunctions

Incorrect associations of features from different objects when attention is inhibited - Treisman and Schmidt (1982)

• presented character strings very briefly followed by noise mask - “9-green X-blue P- red B-8

• primary task was to report the 2 numbers

• then asked to report coloured letters

• often associated wrong colour with wrong letter = illusory conjunctions

Conjunction Search

Visual search where the target differs from the distractors only by its particular combination of features, requiring attention to be applied to each object in turn = very slow search - requires binding problem to be solved

e.g. finding red horizontal bar in group of red vertical bars and green horizontal bars.

Feature Search

Visual search where the target contains a feature that the distractors do not contain, allowing for a fast search without needing to attend to each item in turn. e.g. red square in group of green squares

Motion Transients

Changes usually generate motion transients that draw attention to the location change, thereby making it easy to spot the change = change blindness doesn’t always occur

what directs our attention

an initial involuntary process (mediated by attentional capture) and then subsequent voluntary process guided by goals and expectations

expectations

after saliency determines what we attend to first, what we attend to is influenced by cognitive factors = goals and expectations

• expectations = if object is unexpected = fixate on it for longer and more often

semantically consistent vs semantically inconsistent object or syntactically inconsistent object

semantically consistent object

An object that fits well within the expected context or scenario

e.g. pan on stove

semantically inconsistent object

An object that does not fit within the expected context or scenario, leading to increased attention e.g. shoe on a stove.

syntactically inconsistent object

An object that violates the expected grammatical structure or sequencing in a given context, resulting in heightened visual attention. e.g. pan that floats above stove

Carrasco et al 2004

Participants were shown two visual stimuli (gratings) with varying contrast levels on either side of a fixation point. A cue (brief flash) directed their attention to one side before the stimuli appeared. Results = attention directed to one side = more often judged the cued stimulus as having higher contrast — even when the two stimuli were physically identical = Covert attention enhances the perceived contrast of a stimulus, showing that attention alters visual appearance

feature integration theory

suggests that binding problem is solved by attending to only one location at a time

Balint’s syndrome

a neurological condition resulting from bilateral damage to the parietal lobes, characterized by an inability to focus attention on multiple objects, leading to misperception of scenes = prone to illusory conjunctions bc can’t focus attention on single object