Visual Selective Attention

Selective Attention

• Attention enables the mind to focus clearly on simultaneously possible objects or trains of thought, according to William James in 1890.
• Selection in attention serves to prioritize a subset of information.
• Selection is needed because the brain receives information from multiple sensory systems
• Selection is needed because not all information received by the brain is relevant at any given time
• Selection is needed because there are physiological limits imposed by effector systems such as eyes and hands.
• Selection occurs because capacity limits are associated with neural function and metabolism; fewer than 10% of cortical neurons spike at any one time (Lennie, 2003).
• The physiology of the visual system constrains the type and amount of information observers obtain from the environment (scene).

Visual Selective Attention

• Visual acuity influences the spatial resolution of information sampled during a single fixation.
• Eye movements are an example of overt attention.
• The decision to fixate can follow a random or guided sequence.
• Covert attention prioritizes areas or objects for action, such as eye movements.
• Covert attention prioritises information for analyses and retention

Post-Perceptual Processes

• Working memory is a post-perceptual process.
• Working memory has a capacity limited temporal store.
• Verbal short-term memory (STM) holds approximately 7 ± 2 items.
• Visual working memory (WM) can hold <= 4 items.

Accuracy of Recall in Selective Attention

• Accuracy of recall is determined by capacity/load multiplied by decay.
• Decay follows an exponential function.
• Selective attention provides access to visual working memory (VWM) to reduce the load.
• Attention enhances accuracy of recall for the selected card.
• Selective attention protects capacity limits via effector systems (action).
• Selective attention protects capacity limits via cognitive systems and cortical computation, like VWM.
• Selection biases perceptual sampling and post-perceptual processes.

Orienting Attention

• Attentional guidance can be exogenous (bottom-up) or endogenous (top-down). Both defined in 1989 by Muller & Rabbitt.

Exogenous Attention

• Exogenous attention is stimulus-driven and involves a bottom-up capture of a salient signal, like a bright flash or loud sound.
• Exogenous attention is involuntary, as it is captured by a non-predictive cue.
• It has a fast rise-time, with peak benefit around 150 ms after cue onset.
• Exogenous attention involves inhibition of return (IOR).

Endogenous Attention

• Endogenous attention is goal-driven, using top-down selection.
• It has a slow rise-time, with peak benefit around 275-400 ms after cue onset.
• Endogenous attention has a long-lasting bias, with no evidence of IOR.

Measuring Attention

• Selective attention is a cognitive construct, a concept used to explain behavior.
• Selective attention is not directly measurable.
• Psychologists manipulate stimuli and measure behavioral or physiological responses to make conclusions about selective attention.

Attention and Spatial Acuity

• Montagna and colleagues (2009) studied the effects of exogenous and endogenous cues on spatial acuity.
• Shifts of attention allocate limited-capacity perceptual resources.
• Spatial acuity at cued locations is greater than uncued baseline.
• Spatial acuity at uncued locations is less than uncued baseline.
• Spatial acuity at a cued location is significantly higher than the uncued baseline.
• There is a concomitant decrease in acuity at the uncued location.
• Covert attention mediates in observer's spatial acuity in the absence of eye movements

Attention and Signal-to-Noise

• Previous studies presented stimuli very fast to create discrimination difficult.
• Objects outside the lab are often accompanied by noise.
• Noise can include occluding objects in visual scenes and competing voices in auditory scenes.
• Dosher & Lu investigated whether attention has a "noise-exclusion" mechanism.
• The discriminability of the target at cued locations was higher than that at uncued locations.
• The affect of cueing was more pronounced in displays containing high levels of external noise.
• Selective attention increases detection at cued location by increasing the signal-to-noise ratio.

Auditory Selective Attention

• Spence & Driver (1997; 1994) studied the benefits of auditory spatial attention using an "orthogonal" cueing paradigm.
• Selective auditory attention:
  • Increases spatial acuity of auditory localization.
  • Increases acuity of non-spatial judgements (pitch).
  • Protects selected items from degradation in auditory working memory.
• Exogenous and endogenous cues both produce similar benefits, but have different time courses.

Summary

• Selective attention is a set of processes that protect capacity-limited perceptual and post-perceptual resources.
• Shifts of spatial attention can be triggered exogenously or endogenously.
• Covert spatial attention:
  • Increases spatial resolution.
  • Increases signal-to-noise ratio.
  • Combines sensory information across modalities.