Characteristics of Human Luminance Discrimination and Modeling a Neural Network Based on the Response Properties of the Visual Cortex (original) (raw)
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Cortical visual processing is temporally dispersed by luminance in human subjects
Neuroscience Letters, 1999
Increasing the intensity of a stimulus such as luminance results in faster processing of the signal and therefore decreases simple motor reaction time (RT). We studied the latencies of visual evoked potentials (VEPs, N80, P100, N130) and RTs in eight subjects to flashing spots of light while varying the luminance of the spots from 1 to 1000 cd/m 2 . The data show that processing time as a function of intensity is modified not only at the retina but also at later processing sites. This indicates a temporal dispersion of the visual signal over the whole processing stream from visual input all the way to motor output.
Journal of the Optical Society of America A, 1987
Relations between luminance contrast and reaction time were studied for foveal vision over a three-decade range of background luminance. On each background, the contrast equivalence relation between negative and positive contrast flashes conformed almost exactly to the result expected if equal luminance steps of opposite sign produce equal visual effects. The same result held for threshold detection for flashes of variable duration. Analysis of these data suggests that reaction time is triggered by the early, rising phase of an internal response and that the effective stimulus energy that triggers the response is only moderately suprathreshold. On all backgrounds the sensory latency for reaction time (L) was described reasonably well by the relation L = bS-0 . 67 , where b is constant and S is the absolute value of the luminance step. This implies that reaction time is largely independent of contrast polarity and the background luminance. Parallels between the present results and recent intracellular work suggest that the contrast equivalence relation for reaction time is largely shaped by early linear mechanisms in cones.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience
Decisions about the visual world can take time to form, especially when information is unreliable. We studied the neural correlate of gradual decision formation by recording activity from the lateral intraparietal cortex (area LIP) of rhesus monkeys during a combined motion-discrimination reaction-time task. Monkeys reported the direction of random-dot motion by making an eye movement to one of two peripheral choice targets, one of which was within the response field of the neuron. We varied the difficulty of the task and measured both the accuracy of direction discrimination and the time required to reach a decision. Both the accuracy and speed of decisions increased as a function of motion strength. During the period of decision formation, the epoch between onset of visual motion and the initiation of the eye movement response, LIP neurons underwent ramp-like changes in their discharge rate that predicted the monkey's decision. A steeper rise in spike rate was associated with ...
The Journal of neuroscience : the official journal of the Society for Neuroscience, 2002
Decisions about the visual world can take time to form, especially when information is unreliable. We studied the neural correlate of gradual decision formation by recording activity from the lateral intraparietal cortex (area LIP) of rhesus monkeys during a combined motion-discrimination reaction-time task. Monkeys reported the direction of random-dot motion by making an eye movement to one of two peripheral choice targets, one of which was within the response field of the neuron. We varied the difficulty of the task and measured both the accuracy of direction discrimination and the time required to reach a decision. Both the accuracy and speed of decisions increased as a function of motion strength. During the period of decision formation, the epoch between onset of visual motion and the initiation of the eye movement response, LIP neurons underwent ramp-like changes in their discharge rate that predicted the monkey's decision. A steeper rise in spike rate was associated with ...
Purpose: Previous studies have suggested that compared to first-order (FO) motion stimuli, second-order (SO) motion stimuli required more cortical time to be processed. The purpose of this study was: 1-to verify this claim with Visual Evoked Potential (VEP) and eye-hand Reaction Time (RT) measurements and 2-examine if the VEP and RT responses are similarly modulated by the same trigger features of the stimuli. Methods: The VEPs and eye-hand RT for motion-reversal luminance-(first-order) and texturedefined (second-order) stimuli were recorded from ten normal human subjects. VEPs and RTs were measured for each motion class at eight different modulation depths (from 3 to 100%). Results: Our results reveal that for stimuli of low contrast levels, the SO-FO timing differences are approximately 100 ms (RT) or 20 ms (VEP), while for contrasts ‡ 15-20% (VEP) or ‡ 50% (RT), the SO-FO difference is no longer significant (p > 0.007), suggesting either that the brain can no longer distinguish SO from FO stimuli or that in spite of the added complexity of SO stimuli the brain takes equal time to process both. Conclusion: Interestingly, the above contrast discrepancy in SO-FO resolution threshold suggests that, compared to the VEP, the more psychophysical RT measurement can process and thus distinguish a larger spectrum of motion stimuli, thus further confirming the latter measure of the retinocortical processing time as a valid alternative to the VEP.
V1 neurons respond to luminance changes faster than contrast changes
Scientific reports, 2015
Luminance and contrast are two major attributes of objects in the visual scene. Luminance and contrast information received by visual neurons are often updated simultaneously. We examined the temporal response properties of neurons in the primary visual cortex (V1) to stimuli whose luminance and contrast were simultaneously changed by 50 Hz. We found that response tuning to luminance changes precedes tuning to contrast changes in V1. For most V1 neurons, the onset time of response tuning to luminance changes was shorter than that to contrast changes. Most neurons carried luminance information in the early response stage, while all neurons carried both contrast and luminance information in the late response stage. The early luminance response suggests that cortical processing for luminance is not as slow as previously thought.
A Model of Neuronal Responses in Visual
1998
Electrophysiological studies indicate that neurons in the middle temporal (MT) area of the primate brain are selective for the velocity of visual stimuli. This paper describes a computational model of MT physiology, in which local image velocities are represented via the distribution of MT neuronal responses. The computation is performed in two stages, corresponding to neurons in cortical areas V1 and MT. Each stage computes a weighted linear sum of inputs, followed by rectification and divisive normalization. V1 receptive field weights are designed for orientation and direction selectivity. MT receptive field weights are designed for velocity (both speed and direction) selectivity. The paper includes computational simulations accounting for a wide range of physiological data, and describes experiments that could be used to further test and refine the model.
Temporal precision in the neural code and the timescales of natural vision
Nature, 2007
The timing of action potentials relative to sensory stimuli can be precise down to milliseconds in the visual system 1-7 , even though the relevant timescales of natural vision are much slower. The existence of such precision contributes to a fundamental debate over the basis of the neural code and, specifically, what timescales are important for neural computation . Using recordings in the lateral geniculate nucleus, here we demonstrate that the relevant timescale of neuronal spike trains depends on the frequency content of the visual stimulus, and that 'relative', not absolute, precision is maintained both during spatially uniform whitenoise visual stimuli and naturalistic movies. Using informationtheoretic techniques, we demonstrate a clear role of relative precision, and show that the experimentally observed temporal structure in the neuronal response is necessary to represent accurately the more slowly changing visual world. By establishing a functional role of precision, we link visual neuron function on slow timescales to temporal structure in the response at faster timescales, and uncover a straightforward purpose of finetimescale features of neuronal spike trains. illustrates one of the many contexts in which millisecond precision has been observed in neuronal responses, showing the response of a geniculate neuron to repeated presentations of a spatially uniform white-noise visual stimulus (SUN). This remarkable precision at millisecond timescales has been observed in the retina 2,7 , the lateral geniculate nucleus (LGN) 5,6 and the visual cortex 1,3,10 as well as in many other sensory systems such as the fly visual system 4,9 , the electrosensory system of the weakly electric fish 11 , and the mammalian somatosensory 12,13 and auditory systems 14 . Although the presence of such fine temporal structure in the neuronal response would not be surprising if the sensory stimulus had similar temporal structure, its role is less clear in the mammalian visual system in which relevant visual stimuli are typically on much slower timescales. In particular, visual perception is ultimately limited by the relatively slow integration time of photoreceptors, which, for example, results in the appearance of continuous motion from the flickering images that constitute a movie. As a result, the much finer temporal structure in visual neuron responses has been proposed to be evidence for 'temporal encoding', which postulates that particular temporal patterns in the spike train carry additional information about the visual stimulus 8,15 .