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Davis M. Glasser, Duje Tadin; The oculomotor system can discriminate perceptually suppressed motion: an oculometric analysis. Journal of Vision 2012;12(9):994. doi: 10.1167/12.9.994.
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© ARVO (1962-2015); The Authors (2016-present)
The ocular following response (OFR) is a reflexive eye movement that occurs in response to large, high-contrast, and rapidly moving stimuli with an abrupt onset (Miles, Kawano, & Optican, 1986). It is believed to support the stabilization of the retinal image, especially after saccades. The stimulus conditions that optimally evoke the OFR are also favorable for eliciting behavioral spatial suppression (Tadin, Lappin, Gilroy, & Blake, 2003). That is, increasing the size of a high-contrast moving stimulus makes its motion harder to discriminate – but these same manipulations should also increase the magnitude and directional selectivity of the OFR. This disconnect between perceptual and oculomotor size tuning led us to hypothesize that perceptually suppressed stimuli would nonetheless yield measurable OFRs. To investigate this relationship, we presented observers with brief (67 ms), large (radius = 8º), high-contrast, rapidly moving (TF=16Hz) grating stimuli. We measured observers’ psychophysical judgments of stimulus motion direction while simultaneously recording reflexive eye movements evoked by the same stimuli. As expected from our previous work, observers were unable to discriminate the direction of stimulus motion at above chance levels. However, these stimuli induced reliable OFRs that matched previously reported latencies and amplitudes. Specifically, for perceptually at-chance moving stimuli, OFR deflections predicted stimulus direction at ~0.75 probability. In the second experiment, we used signal detection theory to directly compare occulomotor and perceptual sensitivity to these brief moving stimuli. We repeated the above-described measurements across a range of stimulus durations to directly compare psychometric and oculometric functions for the same stimuli. The results revealed that occulomotor threshold were consistently lower than perceptual thresholds. Overall, these findings suggest that the oculomotor system has access to perceptually suppressed motion information. Finally, this conclusion indicates that the neural mechanisms underlying behavioral spatial suppression lie either subsequent or in parallel to those underlying the OFR.
Meeting abstract presented at VSS 2012
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