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Jelmer P. de Vries, Ignace T. C. Hooge, Marco A. Wiering, Frans. A. J. Verstraten; Saccadic target selection and temporal properties of visual encoding. Journal of Vision 2010;10(7):499. doi: https://doi.org/10.1167/10.7.499.
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© ARVO (1962-2015); The Authors (2016-present)
Literature shows many tasks in which saccades following short latencies tend to land on salient elements, while those following longer latencies more frequently land on elements similar to the target. This has given rise to the idea that independent bottom-up and top-down processes govern saccadic targeting. Recent findings, however, show that even when the target of a search is the most salient element, the tendency to saccade towards this target decreases as latencies prolong. It is difficult to explain these findings in terms of bottom-up and top-down processes. We investigated whether temporal differences in encoding of peripheral visual information can explain this finding. The visual system processes low spatial frequency (LSF) information faster than high spatial frequency (HSF) information. Similarly, high contrast information is processed faster than low contrast information. The stimuli in our experiments contained two deviating targets on a homogenous grid of non-targets. In the first experiment, one target deviates in its low spatial frequencies, the other target in its high spatial frequencies. The task of the subject was to make a speeded saccade towards either target. For the short saccade latencies, a bias towards the low frequency target was found. Interestingly, with increasing latency this bias disappeared and both targets were selected equally frequent. These results suggest a link between temporal aspects of encoding and saccadic targeting. In the second experiment we further tested this theory by varying the contrast of the LSF target. In one condition we raised the contrast of the LSF target, resulting in an increase in the bias towards this target. Lowering the contrast of the LSF target in a second condition resulted in a shift in bias towards the HSF target. These experiments provide converging evidence that temporal aspects of encoding underlie saccadic target selection.
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