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Alan Freeman, Gloria Luo-Li, David Alais; The psychophysicist’s microscope: weak stimuli reveal neuron-like response properties. Journal of Vision 2015;15(12):256. doi: 10.1167/15.12.256.
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© 2017 Association for Research in Vision and Ophthalmology.
Aims. 1. The visual contrast-response function in human subjects typically has low gradient at low contrast. This is inconsistent with signal detection theory, and we therefore aimed to measure precisely the contrast-response function at low contrast. 2. Recently published work shows that light decrements are detected sooner than increments. We aimed to see whether this observation held at low contrast. Methods. Visually normal adult humans were briefly presented with horizontal grating patches. The gratings were raised-cosine in form so that each presentation provided either an increment or decrement in luminance. Either the left or right half of the grating patch was shown and subjects indicated which half had been shown. Stimuli were randomly timed, and response correctness and reaction time were recorded. Results. There was a small range of contrasts, centred on zero, at which contrast sensitivity was indistinguishable from zero. Neurons in primary visual cortex have a resting membrane potential well below threshold (Tan et al., Nature, 509, 226): we propose that the contrast sensitivity plateau indicates the minimum contrast required to depolarise these neurons to threshold. Further, reaction times at low contrast were about 50 ms shorter for contrast decrements than for increments. This corresponds well with recently published work showing that off-dominated cortical neurons have shorter latencies to decrements than do on-dominated neurons to increments (Komban et al., Neuron, 82, 224). Conclusion. Low-contrast measurements reveal behaviour that appears to reflect the properties of single neurons in primary visual cortex.
Meeting abstract presented at VSS 2015
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