sensation and perception (attention)

Attention definition

Attention is the ability to preferentially process some parts of a stimulus at the expense of processing of other parts of the stimulus

Eg. If you focus your attention on my face, you will preferentially process my face at the expense of processing other objects in the scene.

Consequently, you will perceive my face more clearly than other objects in this scene

Visual attention

Perceptual system has limited capacity

Can’t process everything in the visual scene simultaneously

For example, in front of me now there are lots of people, can’t look at everyone at the same time. To avoid being overwhelmed, I pay attention to only one person at a time and ignore the rest.

Attention therefore helps us avoid becoming overwhelmed.

Overt attention

Overt attention involves looking directly at an object

Covert attention

Covert attention involves looking at one object but attending to another object

Monitoring attention

Can generally tell where someone is attending just by tracking their eye movements.

When a person looks at an object, they are said to fixate it.

The eye movements between fixations are ballistic

Eye movements are called saccades

Ballistic fixation

Rest between jumps (saccades) are known as fixations - eyes stay looking at one part of the scene

(Fixation determined by your goals and expectations)

Saccade

Eye jump from point to point - eyes do not scan over a visual scene smoothly

Attentional capture

Determined by salience of image/object

Eg. Attention drawn to red matchstick in a bunch of black matchsticks

Salience

Quality of being noticeable

Eg. Different colour, different size

What captures our attention

Contrast:

• Regions of colour contrast or luminance contrast

• Regions of size contrast

• Regions orientation contrast

• Regions of motion/flicker contrast

What directs our attention?

Salience determines what we attend to first

After that we attend to is determined by cognitive factors such as the observer’s goals and expectations

Expectations

Fixations not only determined by goals; expectations also determine fixation

Unexpected object will make you fixate on it longer and more often

Attention can change the appearance of an object

Attention makes perception more vivid

Attention affects not only how quickly a person can respond to a stimulus but also the appearance of the stimulus

Attention can influence physiological responding

Affect physiological response to a stimulus

Neurons in the brain respond more strongly to attended stimuli than to unattended stimuli

Attended stimuli

What you’re focusing on

Unattended stimuli

Other objects in your field of vision that your brain filters out when focusing on something

Why is attention needed?

Helps the brain focus on important information and filter out distractions. There’s too much going on around us at once - attention makes sure we don’t get overwhelmed and can respond to what matters most

What directs your attention?

Directed by external factors and internal factors:

Involuntary factors; determined by saliency of the scene ie sudden noises, bright lights, movement (attentional capture)

Voluntary factors - your goals and expectations

What are the effects of attention?

Attention speeds responses

Attention can influence appearance

Attention can influence physiological responding

Binding problem

Different aspects of a stimulus are processed independently, often in separate brain areas.

Eg. Motion processed in dorsal stream; form is processed by ventral stream

The issue of how any object’s individual features are combined (ie bound) to create a coherent perception is known as the binding problem.

Feature integration theory

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

Only features associated with that location are processed, so only those features are bound together

Avoids binding features from different objects

Illusory conjunctions

Incorrect bindings - ie wrong colour to wrong object

A prediction of FIT is that if attention is inhibited, features from different objects will be incorrectly bound together

Balint’s Syndrome

Cannot focus attention on just a single object

Parietal lobe damage

When multiple objects are present, patient has difficulty focusing attention on single object

Report wrong letter colour combination on 23% of trials even when viewing letters for up to 10 seconds

Visual search - finding an object in a bunch of other objects like red square in a bunch of green squares

Visual searches that require binding problem - slow

Eg. Horizontal green, vertical and horizontal red

Visual searches that don’t require binding problem - fast

Eg. Red square, green square

Change blindness

Determine what you remember from the picture

If you don’t attend to it, chances are you won’t remember it

Can only remember a few parts of a scene at one time - if one of those parts change, you notice the change, if some other parts of the scene changes, chances are you won’t notice the change - change blindness

Motion transients

Generate motion that draw attention to the location change, making it easier to spot the change

Eg. In first demonstration, blank screen was inserted between images. Meant that when second image shown, motion transient occurs for every part of the image - not just parts that changed - motion transient did not guide attention to the change