A new tool that may measure certain absolute temporal properties of information processing in intact organisms is suggested by. investigations of temporal summation in single nerve cells. Two findings have led to this suggestion: One, the form of the temporal summation function (relating the intensity and duration required to evoke a criterion neural signal) depends on the analysis used by the investigator. Corresponding form variations occur in behavioral studies when the observer's task is varied. Two, the critical durations of fixed neural signals depend on the latency of the feature of the signal chosen as criterion; early features yield short critical durations and vice versa. The critical duration also varies in behavioral studies if one varies the observer's task, keeping the stimulus ensemble fixed.These data lead to two inferences: One, the form of a behavioral temporal-summation function expresses the kind of hidden mental analysis mediating that behavior. Two, a behavioral critical duration is an indicator of the absolute timing of the hidden mental analysis mediating that behavior.

Short light flashes can appear brighter than longer flashes. This brightness enhancement has often been attributed to neural transients occurring shortly after stimulus onset. This attribution assumes an equivalence between the totality of the response to a stimulus of a given duration and the instantaneous response at a given time after stimulus onset. Recordings from Limulus photoreceptors indicate that this attribution is an example of illusory correlation.

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The compound eye of the grasshopper Phlaeoba has alternating bands that appear clear or brown. Electroretinograms recorded from the individual bands have different action spectra: The spectrum of the clear band peaks at 525 nanometers and that of the brown band at 545 nanometers. Spectrally selective whole-eye adaptation with light of eight long of short wavelength yields identical action spectra. This evidence suggests that this eye has only one visual pigment, whose spectrum is altered in the brown bands by a screening pigment. In behavioral tests of spontaneous choices between stimuli that appear green to the normal human and those that appear red, the green stimuli are preferred even when the relative intensity is varied by 0.9 log units around the equal-brightness level (determined by the electroretinogram). When some red light is mixed with the green light, the preference for the mixture is less than for the green light alone, even though the mixture is more intense. True color vision therefore seems to exist. Painting the bands shows that behavioral color vision requires the presence of both types. These data suggest that Phlaeoba has true color vision mediated by one visual pigment and suitable optical filters.

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