Covert attention increases contrast sensitivity: psychophysical, neurophysiological and neuroimaging studies

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Abstract

This chapter focuses on the effect of covert spatial attention on contrast sensitivity, a basic visual dimension where the best mechanistic understanding of attention has been achieved. I discuss how models of contrast sensitivity, as well as the confluence of psychophysical, single-unit recording, and neuroimaging studies, suggest that attention increases contrast sensitivity via contrast gain, an effect akin to a change in the physical contrast stimulus. I suggest possible research directions and ways to strengthen the interaction among different levels of analysis to further our understanding of visual attention.

Section snippets

Limited resources

Each time we open our eyes we are confronted with an overwhelming amount of information. Despite this fact, we have the clear impression of understanding what we see. This requires selecting relevant information out of the irrelevant noise, selecting the wheat from the chaff. In Funes el Memorioso [Funes the Memoirist], Borges suggests that forgetting is what enables remembering and thinking; in perception, ignoring irrelevant information is what makes it possible for us to attend and interpret

Effects of transient attention on early vision

Much research has focused on the time course and degree of automaticity of the allocation of sustained and transient attention. However, less is known about the ways in which these systems, in particular sustained attention, affect fundamental visual dimensions. In past research, my laboratory has been particularly interested in characterizing the effects of transient attention on early visual processes. Given that transient attention highlights salient changes in the environment, its default,

Neurophysiological studies of attentional modulation of apparent stimulus contrast: attentional facilitation and selection

The development of techniques to record the activity of neurons in awake-behaving animals has enabled researchers to probe the biological foundations of sustained attention. Single-unit recording studies in the monkey have provided detailed, quantitative descriptions of how attention alters visual cortical neuron responses.

A number of neurophysiological studies have shown that directing attention to a stimulus increases neuronal sensitivity, so that neurons respond to an attended stimulus much

Transient attention enhances perceptual performance and fMRI response in human visual cortex

Studies on brain mechanisms of attention have mostly examined sustained attention, and some of them have characterized its effects on stimulus processing in the visual cortex. For instance, in single-unit recording studies, researchers have learned that sustained attention can reduce external noise by reducing the influence of unattended stimuli (Moran and Desimone, 1985; Luck et al., 1997) and that it can also boost the signal by increasing the effective stimulus contrast (Reynolds et al., 2000

Conclusion

As remarkable as the human visual and cognitive systems may be, inevitably we are still limited by both bandwidth and processing power. There is a fixed amount of overall energy consumption available to the brain, and the cost of cortical computation is high. Attention is crucial in optimizing the systems’ limited resources.

This chapter has focused on the effects of spatial attention on contrast sensitivity, for which the best mechanistic understanding of visual attention has been achieved due

Acknowledgments

We thank the past and present lab members, in particular Leslie Cameron, Sam Ling, Taosheng Liu, Cigdem Penpeci-Talgar, and Franco Pestilli, coauthors in the psychophysical and neuroimaging research described here, to Stuart Fuller, Sam Ling, Taosheng Liu, and Franco Pestilli, for helpful comments on this manuscript, and to John Reynolds and Stephan Treue for allowing us to reprint figures from their papers.

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