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.

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.

Treatment of psoriasis with orally administered 8-methoxypsoralen and long-wavelength ultraviolet radiation.

Between May 1976 and September 1977, 51 patients with severe psoriasis were treated with orally administered 8-methoxypsoralen followed by exposure to high-intensity long-wavelength ultraviolet radiation. Clearing of psoriasis occurred in 40 patients (78%) and marked improvement in 5 (10%). Of the remaining patients three (6%), who had generalized erythroderma, failed to respond to this therapy.

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.

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.

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.

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.

Photosensitivity: results of investigation in 250 patients.

Between January 1972 and December 1974, 250 patients were referred for investigation of possible photosensitivity to a university-associated clinical research unit for photobiology. In addition to an appropriate history and clinical examination, phototesting was carried out with a solar simulator, monochromatic light and fluorescent light directed to patch-tested areas of skin. Photosensitivity was not demonstrated in 110 patients (44%).

Lomotil ingestions in children.

Although the incidence of adverse reactions is relatively low in adults, Lomotil may result in serious toxicity in children. Early effects are often due to the atropine present in the compound, while the narcotic-like actions of diphenoxylate HCI tend to occur later. Respiratory depression is the most threatening reaction and should be treated with naloxone.

Limulus psychophysics: dark adaptation in the ventral eye.

Sudden illumination applied to Limulus produces an unconditioned downward tail movement which is under stimulus control and can be used to measure psychophysical thresholds. The method of constant stimuli was used to measure the behavioral dark-adaptation function mediated by the ventral eye of Limulus. The resulting function has two phases, each of which is rectified when log threshold is made a function of long time in the dark.

Illusory correlation of brightness enhancement and transients in the nervous system.

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.