Contributions from cognitive neuroscience to understanding functional mechanisms of visual search

Abstract

We argue that cognitive neuroscience can contribute not only information about the neural localization of processes underlying visual search, but also information about the functional nature of these processes. First we present an overview of recent work on whether search for form–colour conjunctions is constrained by processes involved in binding across the two dimensions. Patients with parietal lesions show a selective problem with form–colour conjunctive search relative to a more difficult search task not requiring cross-dimensional binding. This is consistent with an additional process—cross-dimensional binding—being involved in the conjunctive search task. We then review evidence from preview search using electrophysiological, brain imaging, and neuropsychological techniques suggesting preview benefits in search are not simply due to onset capture. Taken together the results highlight the value of using converging evidence from behavioural studies of normal observers and studies using neuroscientific methods.

Acknowledgments

This work was supported by grants from the BBSRC and MRC UK and by the British Council/NWO.

Notes

¹Reaction times (RTs) were measured. When there are slow RTs in search, there may be some rate-limiting factor (e.g., the ability to discriminate the target from a distractor) that constrains performance even if TMS had an effect on other processes (e.g., the speed of serially selecting each stimulus for subsequent discrimination). For example, if the time to discriminate the target from the distractor is sufficiently long and variable, then there may be negligible effects due to changing the speed of selecting each item for discrimination.

²We have also found this same pattern, of an onset advantage in terms of an intercept rather than a slope effect, in controls matched in age to the patients. It may be that competition from onsets and offsets becomes closer as participants age.