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Abstract:
We wished to study the influence of attention to colour and
form on visual processing. Adult subjects (n=12) completed a series
of tasks in which they detected targets as a function of shape
and/or colour features. The target differed in each task: task #1,
the target was discriminated by shape, colour was held constant;
task #2, the target was discriminated by colour, shape was
constant; task #3, the target required discrimination of a
conjunction of features, colour and shape; task #4 (redundant task)
the target could be discriminated using either feature. Subjects
pressed 'yes' for targets and 'no' to non-targets. The N2 ERP
component was very prominent at posterior temporal sites (P9 and
P10) and differed with tasks. N2 latencies were shorter for targets
than non-targets, and longest for task 2 (discrimination by
colour). N2 amplitudes were equivalent for targets and non-targets
in task 2; this was also the case in the redundant task, suggesting
that subjects used colour for target discrimination, when they had
the choice. N2 amplitudes were larger over P9 (left hemisphere)
than P10 (right hemisphere) when subjects had to use shape
discrimination (tasks 1 and 3). Both shape and colour are processed
primarily by the ventral visual pathway; the current data suggest
that this processing is faster and more lateralised when the
critical information is shape.
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