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BVI Seminar: Attentional selection of colour is determined by both cone-based and hue-based representations
June 9 @ 4:00 pm - 5:00 pm
Jasna Martinovic, University of Aberdeen
What is the nature of representations that sustain attention to colour? In other words, is attention to colour predominantly determined by the low-level, cone-opponent chromatic mechanisms established at subcortical processing stages, or by the multiple narrowly-tuned higher-level chromatic mechanisms established in the cortex? These questions remain unresolved in spite of decades of research. In an attempt to address this problem, we conducted a series of electroencephalographic (EEG) studies that examined cone-opponent and hue-based contributions to colour selection. We used a feature-based attention paradigm, in which spatially overlapping, flickering random dot kinematograms (RDKs) of different colours are presented and participants are asked to selectively attend to a colour in order to detect brief, coherent motion intervals, ignoring any such events in the unattended colours. Each flickering colour drives a separate steady-state visual evoked potential (SSVEP), a response whose amplitude increases when that colour is attended. In our studies, behavioural performance and SSVEPs are thus taken as indicators of selective attention. The first study demonstrated that at least some of the observed cone-opponent attentional effects can be explained by asymmetric summation of signals from different cone-opponent channels with luminance at early cortical sites (V1-V3). This indicates that there might be cone-mechanism-specific optimal contrast ranges for combining colour and luminance signals. The second study demonstrated that hue-based contributions can also be observed concurrently with the aforementioned low-level, cone-opponent effects. Proximity and linear separability of targets and distractors in a hue-based colour space was shown to be another determinant of effective colour selection. In conclusion, attention to colour should be examined across the full range of chromoluminance space, task space and dependent measure space. Current evidence indicates that multiple representations contribute to selection of colour, and that depending on the stimulus attributes, task demands, and the attributes of the applied measures, it is possible to observe a spectrum of effects ranging from purely cone-opponent to largely hue-based.
Dr Jasna Martinovic is a senior lecturer at the University of Aberdeen. She completed her PhD at the University of Leipzig, followed by postdoctoral work at the University of Liverpool. Her research investigates how colour and luminance signals feed into mid and higher-level stages of visual perception, as well as how they are sampled by visual attention.