Sensation and Perception: Attention

Attention

• Attention is preferentially processing some stimuli at the cost of processing other parts
• Helps to perceive the attended stimuli better than the rest of the objects
• Needed because the perceptual system has a limited capacity and cannot process everything in the visual scene simultaneously

Types of Attention

• Overt attention: involves looking directly at an object
• Covert attention: involves looking at one object but attending to another object

Monitoring Attention

• Unless you purposely try not to, you tend to fixate the object to which you attend
• Fixate is when someone looks at an object
• What you fixate on depends on your goals and expectations
• Saccades are the ballistic eye movements between these fixations
• During saccades, you become temporarily blind

Directing Attention

• Two processes:
  • Initial involuntary process: mediated by attentional capture (e.g., sudden change on TV)
  • Subsequent voluntary process: guided by goals and expectations

Salience

• Determined by the salience of an image or object
• Salience is the quality of being noticeable
• What captures our attention:
  • High contrast (colour, luminance, size, orientation, motion/flicker)
  • Fixations are not only determined by goals but also expectations

Effects of Attention

• Speeds responses
• Influences appearance
• Influences physiological responding

The Binding Problem

• Different aspects of a stimulus are processed independently in separate brain areas
• Issue of how an object's individual features are combined to create a coherent percept
• Feature integration theory (FIT):
  • Suggests that this problem is solved by attending to only one location at a time
  • Features associated with that location are processed and bound together
  • Avoids binding features from different objects
• Illusory conjunctions: predicts that if attention is inhibited, features from different objects will be incorrectly bound
• Balint's syndrome: a patient with parietal lobe damage is prone to experiencing illusory conjunctions

Visual Search

• Some form of visual search is required for binding to occur
• Conjunction search: target object contains the same features as distractors
• FIT suggests that undivided attention is needed to understand each object's integration, making conjunction search slow
• Feature search: finding a target object with a unique feature that distractors don't have, making it faster

Change Blindness

• Attention determines what we remember
• We can only remember a part of the scene at a time
• If part of the scene changes, we may not notice it if attention is not drawn to the location of change