Showing papers on "Summation published in 1977"

Bilateral spatial summation of cooling of symmetrical sites

Abstract: The possibility of spatial summation of conducted −‡Ts (temperature decrements from the adapted skin temperature) was tested when the −‡Ts were presented simultaneously and individually at symmetrical sites on either side of the body. The use of a signal detection rating method yielded data that indicate that spatial summation is complete (area and intensity trade reciprocally) for −‡s near threshold and at clearly suprathreshold intensities of stimulation is invariant of the adapted skin temperature (AT), and the intensity of stimulation within the range of stimuli used (from as little as −0.05‡C to as much as −1.25‡C). In view of the characteristics ascribed to the thermosensory apparatus in humans, it is postulated that spatial summation occurs in the central nervous system.

Analysis of a Network of Electrically Coupled Neurons Producing Rhythmic Activity in the Snail Helisoma Trivolvis

Abstract: This paper deals with a quantitative analysis of a network of electrically coupled neurons (cyberchrons) in the snail Helisoma trivolvis. This network produces regular bursts of activity which drive the motoneurons controlling the feeding musculature. Analysis of the time constants and Bode plots obtained from current injection leads to the development of an equivalent model circuit describing the functional relationships of the individual neuronal elements. The equivalent model is used to demonstrate compensation of the frequency response of an individual neuron by the effective loading of the rest of the network. However, the current observed in a postsynaptic neuron is intergrated across the long cell time constant resulting in increased temporal and spatial summation. This frequency compensation and long duration of the postsynaptic response are both believed to be instrumental in the maintenance of a high frequency burst. This model will act as a framework on which active properties such as burst form, timing, and termination can be tested.

Spatial summation and light adaptation in the goldfish visual system.

Abstract: IN attempting to explain how visual acuity improves as illumination increases, Pirenne and Denton1 suggested that the retinal image is sampled by numerous units, each summing the effects of light over a region of the retina. At very low luminances, only units with the largest summation areas are functional, but with increasing luminance smaller units come into play as their thresholds are exceeded. Since that suggestion was made, cells at all levels of the visual system have been studied electrophysiologically and many receptive fields have been described that might form the basis for such units. Goldfish and other cyprinid fishes, have been the subjects of many such studies, and their retinal synaptic connections have been revealed in detail. I report here some psychophysical experiments which show the effects of light adaptation on spatial summation in the goldfish. The results are consistent with the connections made by rods and cones in the cyprinid retina, and with the theory of a progressive recruitment of ganglion cells with smaller receptive field centres as background luminance is raised.

Temporal summation of the acoustic reflex.

Abstract: A signal-averaging technique was used to minimize acoustic reflex measurement system noise while preserving temporal fidelity. In normal listeners, the interaction of signal intensity and signal duration was explored at visual detection threshold (VDT) and at varying suprathreshold signal levels. Reflex amplitude increases, with signal intensity, at a rate which changes as a function of signal duration, a finding which complicates the interpretation of temporal summation data based on VDT. A theoretical model is proposed to explain the complex interactions of signal intensity, duration, and band width on the amplitude of the acoustic reflex.