Sensory processes最新文献

Temporal summation of vibrotactile stimuli was measured at four frequencies (25, 40, 80, and 160 Hz) using a large contactor. Stimulation at 160 Hz gave temporal summation comparable in amount to that reported in previous studies. Stimulation at 25, 40, and 80 Hz gave less summation. The presence of summation at low frequencies is unexpected in view of existing data obtained with small contactors' those data indicate that the afferent system primarily sensitive to low frequencies may not summate stimulus energy over time. The present data suggest either that the low-frequency afferents do summate energy over time or that, under some conditions, the perception of low-frequency signals presented through a large contactor may be mediated by more than one afferent system.

Three experiments explored the olfactory and the common chemical attributes of sensations produced by various concentrations of n-butyl alcohol. These two attributes combine in an almost-linear fashion to produce the overall perceived intensity of the stimulus. Common chemical intensity makes only a small contribution to overall magnitude at low concentrations, but its proportional contribution increases with concentration. In like manner, speed of response (i.e., reciprocal of reaction time) to the common chemical attribute increases more rapidly than that to odor. Nevertheless, odor always makes its appearance sooner than the common chemical attribute, even when the two attributes are matched in perceived magnitude. Repeated inhalations cause odor intensity to decrease slightly but cause common chemical intensity to increase dramatically. The results obtained from the normal subjects studied here agree with those obtained from subjects with unilateral destruction of the trigeminal nerve.

A human transient-like visual response has been revealed psychophysically with a rotating windmill target, similar to that used by Werblin in his recent studies of the retina of Necturus. The windmill pattern evoked complex perceptual phenomena (important in and of themselves) which were minimized by using a high luminance for the "criterion" flashing test field (relative to its increment threshold), and by moving the four-vaned windmill pattern at a rate of two complete revolutions per second. The transient response, herein defined as the difference in threshold between the stationary and moving windmill conditions, was greatest when the windmill vanes fell completely within the sensitization (inhibition-like) portion of the Westheimer function determined at the same retinal locus. The test has been developed so that it may be readily adapted to available clinical equipment for future diagnostic purposes .

Masked and quiet thresholds at several frequencies of vibratory stimuli were measured as a function of contactor area. The test site was the left index finger; the masking site was the left little finger. The quiet threshold data were consistent with previous investigations: Low-frequency stimuli showed no spatial summation, whereas high-frequency stimuli did. In the presence of a masker, spatial summation was reduced or eliminated for high-frequency stimuli, i.e., the masked threshold was, under some conditions, independent of contactor area. Low-frequency stimuli continued to show no spatial summation in the presence of a masker. The attenuation of spatial summation appears to be a direct function of the intensity of the masking stimulus. Additional measurements with the left thenar eminence as the test site showed that spatial summation could be attenuated by a masker placed on a contralateral body site. The implications of the results for quantifying the effectiveness of a masking stimulus, for the duplex mechanoreceptor hypothesis, and for the nature of spatial summation on the skin are discussed.

Psychophysical thresholds were measured as the frequency, size and duration of vibration on the thenar eminence was varied. The results supported the theory that there are two functionally distinct receptor systems in the skin for the perception of mechanical disturbances. Spatial and temporal summation were found for the detection of high- but not low-frequency stimuli. Furthermore, magnitude estimation data revealed that temporal summation occurs for the perception of high-frequency stimuli presented over a wide range of suprathershold values. On the other hand, temporal summation was absent for low frequency stimuli that were presented at 5, 10, 15, and 20 db above threshold.

It has previously been shown that the reaction time (RT) to radiant heat measures spatial summation of warmth, because the RT decreases with increases in both the areal extent and the intensity (flux density) of the heat. The previous studies of RT let the response terminate the stimulus exposure and thus introduced a confounding between stimulus duration and intensity, since the weaker the stimulus is, the longer it is presented. The present study shows the RT reflects spatial summation even with a fixed, brief stimulus duration. The precise rules for trading area and intensity that are obtained with fixed-duration pulses differ from those obtained with response-terminated ones, but both sets of functions are consistent with each other and with the results of magnitude estimation if it is assumed that the sensory effect of the heat sums over the stimulus duration, that is, that the RT reflects temporal as well as spatial summation. Two further experiments provide direct evidence for temporal summation.

Events in vision triggered by brief flashes in train prove to be strictly analogous to those generated in the skin by a succession of taps. A requisite condition for their appearance in vision is projection of the flashes into the peripheral retinal field. Experiments are described that establish the general relation between extent of saltatory leaping and degree of retinal eccentricity and between leaping and retinal subtense of stimulus patches. Additionally, a curious "dip" phenomenon and several qualitative experiments in which color has been used to "tag" the saltatory image are reported.

Twenty-four aphasic, nine brain-damaged, and eight non-brain-damaged patients were tested for their ability to associate odors with visual targets. The results of the experiment show that lesions producing aphasia interfere with the ability to match an odor to a directly corresponding visual target. As aphasics with anterior and posterior lesions performed at similar levels in this task, it was not possible to conclude that the observed deficits were specifically related to temporal lobe functions. The severity of the deficit was greater for more massively lesioned aphasics. The exact nature of the deficit was not clear, but review of the literature and differential results obtained for the two experimental tasks suggest that aphasic lesions may interefere with odor identification.

Two experiments explored the interaction of spatial and temporal summation in the perception of radiant heat. The first experiment showed that the absolute threshold for detecting two brief (0.1 sec) pulses of heat, one presented to each side of the forehead, is lower than the threshold for detecting a single pulse, even when the two pulses are separated in time by as muchas 0l75 sec. The second experiment showed that a single, 4-sec pulse of heat presented to one side of the forehead feels no warmer than two successive, 2-sec pulses, one to each side. Spatial and temporal summation appear to take place at least partly in the central nervous system.