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G S Wasserman

Publications and source records attributed to G S Wasserman.

At least 55 records · Page 3Linked to original sources
PubMed1980

Filter-mediated color vision with one visual pigment.

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.

Animals↗
PubMed1979

The psychophysical function: harmonizing Fechner and Stevens.

The methods of Fechner and Stevens for assessing sensation quantity usually yield different psychophysical functions even when all other factors are controlled. In this experiment, corresponding differences occurred when different features of the same sensory receptor signals were analyzed. In the visual system, the receptor potential saturated if the peak but not the area was measured; these results match visual psychophysical functions obtained with the methods of Fechner and Stevens, respectively. This result suggests that both methods are equally valid but that each method yields the particular psychophysical function appropriate for a particular kind of information processing. A novel factor in determining sensation quantity, namely the time used by the observer to make a judgment, is implicated by the data.

Animals↗
PubMed1978

Limulus psychophysics: temporal summation in the ventral eye.

Physiological experiments on the properties of temporal summation in single cells of the peripheral visual system of Limulus have shown that the type of temporal summation and the value of the critical duration depend on the way in which the investigator arbitrarily chooses to analyze the same physiological response. The behavioral expression of temporal summation should therefore depend upon the way in which the central nervous system actually analyzes responses transmitted by peripheral structures as well as upon the nature of these peripheral responses. Accordingly, the present two behavioral experiments investigated the analysis of temporal summation carried out by the central nervous system of Limulus by investigating the psychophysics of temporal summation mediated by the ventral eye. Supersummation occurred in both psychophysical experiments up to critical durations near 4.5 sec, which was approximately the same as the reaction times or latencies of the behavioral responses at threshold. The degree of supersummation was extreme; a fourfold change in stimulus duration required an almost 40,000-fold change in stimulus intensity to remain at threshold. Even though some features of physiologically recorded receptor potentials have critical durations less than 10 msec, these findings suggest that the central nervous system of Limulus can integrate peripheral signals over intervals of many seconds. Since the source of the supersummation is the nonlinearity of the receptor transfer function at high levels, these results also indicate that a behavior at threshold can be mediated by a strong neural response.

Animals↗
PubMed1978

Two linear rules relate the latencies of visual responses to their critical durations.

The latency of a neural response sets a limit on its critical duration since stimulation delivered after a response has already occurred can no longer affect that response. However, this tautologic upper limit does not uniquely define the critical duration. Intracellular recordings from the lateral eye of Limulus yield two linear rules which empirically relate the critical duration of a neural response to its latency: When response magnitude (peak amplitude, spike frequency) is used to construct the temporal summation function, the critical duration is equal to the latency minus a constant. When response latency is used instead, the critical duration of the response latency is equal to the latency divided by a constant.

Animals↗
PubMed1978

Changing response measures alters temporal summation in the receptor and spike potentials of the Limulus lateral eye.

Temporal summation and reciprocity were studied in the retinula and eccentric cells of the excised Limulus lateral eye as a function of variation in response measure: Using the latency instead of the peak of the receptor potential as a response measure produced considerably shorter critical durations. Using the area under the receptor potential as a response measure produced no critical duration up to a stimulus duration of 640 msec; instead, supersummation occurred at long durations. Similar effects were observed in the optic nerve spikes, where the response measures were first spike latency and maximum spike number sampled in time windows that ranged from 40 to 640 msec. The critical durations clearly depended on the response measure used and, when a 640-msec window was used, no critical duration occurred; supersummation again occurred. Increasing the sampling period within which maximum spike number was measured increased the critical duration and changed the formal properties from those characteristic of the receptor potential's peak to those characteristic of the receptor potential's area. The implications of the more central portions of the nervous system using different summation times for different perceptual tasks are discussed; it is suggested that the choice of response measures is crucial in studies of temporal summation.

Animals↗
PubMed1978

Temporal summation in the receptor potential of the Limulus lateral eye: comparison between retinula and eccentric cells.

Temporal summation and reciprocity (Bloch's law) were studied in the receptor potential recorded from the retinula and eccentric cells of the excised Limulus lateral eye. Taking the peak of the receptor potential as the response measure yielded critical durations that ranged between 65 and 170 msec, depending on the cell type and the criterion level of response. At high but not at low response levels, the critical duration is significantly longer in eccentric cells than in retinula cells. Deviations from Bloch's law were found; these deviations were largest at intermediate response levels.

Animals↗
PubMed1976

Limulus psychophysics: spectral sensitivity of the ventral eye.

The ventral eye of Limulus contains only one type of photoreceptor. Behaviors mediated by the ventral eye provide an unambiguous representation of the function of that single-receptor type. Such behaviors can be compared with the results of acute, single-cell investigations to assay for the contributions of candidate neural codes in the regulation of behavior (cf. Uttal, 1973). Using an unconditioned tail movement as the response, the psychophysical spectral sensitivity function mediated by the ventral eye of Limulus was measured. This psychophysical function peaked at 525 nm and showed evidence of strong absorption by the cuticle in the short-wavelength portion of the spectrum. Under the conditions of the present experiment, the threshold was 4.5 quanta absorbed per receptor per msec at 525 nm. The spectral transmission of the ventral eye cuticle was also measured. After correction for cuticle absorption, the psychophysical spectral sensitivity function was compared with previously reported spectral sensitivity functions obtained either from electrophysiologic (Millecchia, Bradbury, and Mauro, 1966; Nolte and Brown, 1970) or from microspectrophotometric (Murry, 1966) recordings from single, isolated ventral eye photoreceptor cells. All three functions exhibit a sensitivity peak near 525 nm; the corrected psychophysical and microspectrophotometric functions both display a second peak near 425 nm. A second experiment confirmed the reliability and validity of the 425-nm peak. The coding implications of these findings were explored. A preliminary finding is that, in dichromatic or trichromatic visual systems, two-peaked receptor spectral sensitivity functions produce central, opponent response systems that are qualitatively the same as those produced by single-peaked receptors.

Animals↗
PubMed1976

Lomotil ingestions.

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Child, Preschool↗