Does the sluggishness of colour perception reflect a limitation in the maximum (slew) rate at which chromatic pathways respond to changes in colour?

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At higher temporal frequencies, the appearance of flickering lights is dominated by a steady average, with some residual disturbance at the flicker frequency. The average appearances of flickering lights that turn rapidly off and slowly on and those that turn slowly on and rapidly off can be very different even when their mean colours and intensities are the same. (We refer to these waveforms as 'sawtooth' stimuli.) These differences, which are unexpected, are important because they can provide unique insights into the underlying processing of visual signals that encode colour. Our initial hypothesis is that the differences are due to chromatic mechanisms being better able to follow slow colour changes than fast ones. As a result, their mean outputs become skewed in the direction of the slow change. For example, a yellow light that repeatedly changes slowly to red but then rapidly to green looks on average more red than a light that changes rapidly to red but slowly to green, which looks more green. This imbalance is inconsistent with many current models of chromatic processing, but can be explained by our model. Specifically, we propose that the rate at which colour mechanisms can signal changes in colour is limited to a particular level. If the rate of change exceeds that level, the output varies only at the limiting rate of change. We call this the 'slew-rate' model. Although the idea of a slew-rate limit is familiar in electronics (for example in the specification of operational amplifiers), it is as far as we know novel in the field of vision research. We propose a series of experiments that are designed to test and develop the slew-rate model. Measurements of chromatic detection and chromatic discrimination will be made to characterize the effects of changing the slopes of the sawtooth waveforms as a function of various stimulus parameters. At each stage, these results will be compared with predictions generated by computer simulations of the slew-rate model. Our goal is to critically evaluate the slew rate model. To what extent can the model account for the data? Can simple modifications to the model better account for the data? Can other types of waveforms be used to critically test the model? Can computer simulations suggest other experiments? In addition to causing changes in the mean colour of sawtooth waveforms, a limiting slew-rate should also make us less sensitive to flicker. Thus, the well-known sluggishness of colour perception may be due to the slew-rate limit rather than the more conventional explanation that colour signals are averaged over time. We will also test this prediction by comparing flicker sensitivity measurements with the sawtooth measurements. Testing the slew-rate model per se is not necessarily the most critical feature of this proposal. Equally critical is the fact that we are generating a new dataset using unconventional stimuli and an unconventional model and approach. This new dataset will be made available to other researchers, and can be used by others in the field as well as ourselves to generate new models of how colour vision works. The primary goal of this proposal is to understand more about how chromatic signals are processed in the human brain and in particular why chromatic signals are processed much more slowly than achromatic ones. Despite the many recent advances in related fields, details about how colour processing in humans work remains relatively little understood.