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Brent R. Beutter, Miguel P. Eckstein, Leland S. Stone; Saccadic and perceptual accuracies in a visual-search detection task are similar over a wide range of external noise levels. Journal of Vision 2002;2(7):543. doi: https://doi.org/10.1167/2.7.543.
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© ARVO (1962-2015); The Authors (2016-present)
For stimuli containing external noise, performance can be limited by both external and internal noise. Previously we showed that, for a high external noise level, the accuracy of the 1st saccade and perception (for matched processing times) in a visual-search detection task are nearly the same (Stone et al, Neuro. Abs. 1999; Beutter et al, ARVO 2000). If saccades and perception share visual neural mechanisms (same receptive fields and internal noise), then changing the external noise level should have similar effects on each. Methods: We recorded eye movements and perceptual responses of 2 observers on a 10AFC search task under 2 conditions. In a long condition (up to 4s), observers made saccades to search the display and we defined the 10AFC saccadic decision as the element location closest to the 1st saccade's endpoint. In a short condition (150ms duration to match saccadic processing time), central fixation was required, and we recorded the 10AFC perceptual decision. The Gaussian-blob target (SD=0.24deg), randomly chosen to be in one of ten 2.4deg boxes (5.9deg eccentricity) with SNRs ranging from 2.1 to 9.6, was added to a Gaussian white-noise background with one of 4 rms contrasts (4.6, 9.4, 18.4, 37.4%). Results: For all 4 external noise levels, the perceptual and saccadic accuracies were similar across all SNRs. The mean (over SNR and observers) relative efficiencies (squared d′ ratio) of the saccadic to the perceptual decision were 1.0, 0.7, 0.6, and 0.7, for the 4 increasing external noise levels . For both saccades and perception, at fixed SNR, accuracy decreased as external noise decreased and was dramatically lower for the lowest noise level. Conclusions: Our data show that saccadic and perceptual decisions are similarly influenced by the ratio of internal to external noise, consistent with detection mechanisms with similar receptive fields and internal noise levels. Our results suggest a shared neural processing stage for both saccades and perception.
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