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Joseph S. Lappin, Bart. G. Borghuis, Duje Tadin, Martin. J.M. Lankheet, Wim A. Grind; Human motion discrimination is constrained by the temporal structure of spike trains early in the visual system. Journal of Vision 2002;2(7):585. doi: https://doi.org/10.1167/2.7.585.
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© ARVO (1962-2015); The Authors (2016-present)
The responses of retinal ganglion and LGN cells to drifting gratings were analyzed as inputs to a motion detector. A cortical motion-detector that correlates spike trains from cells at separate locations must integrate these input signals over time in order to detect their similarity. An algorithm was developed to compute optimal integration times for extracting temporal information from the obtained spike trains. Optimal integration times ranged from 5 to 100 msec, decreasing as the temporal frequency of a drifting grating increased. As expected, firing rates increased with contrast, but optimal integration times generally were independent of both contrast and firing rate.
The temporal structure of these retinal and LGN spike trains constrains the motion sensitivity of cortical cells receiving this input. Thus, the temporal limitations of these input signals should also constrain human motion discrimination.
We examined this hypothesis psychophysically by measuring minimum stimulus durations required for human observers to discriminate motion directions. The stimuli were foveal Gabor patches containing a drifting grating (sigma = 10arcmin, SF = 3c/deg, TF = 0.5–20Hz, contrast = 4.6–92%, vertically oriented, random starting phase). Observers discriminated left vs. right motions. Duration thresholds ranged from 4 to 80 msec, decreasing with increases in temporal frequency and independent of contrast. These psychophysical thresholds behaved the same way as the optimal integration times computed from the neural spike trains. Evidently, the temporal thresholds for motion discrimination follow the limits imposed by the temporal structure of spike trains early in the visual system.
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