Sensory processes最新文献

Brightness contrast effects shown by single cells in the macaque's lateral geniculate nucleus were studied with black and white lines of various widths, consisting of either: (1) "simultaneous contrast" stimuli in which the line was produced by luminance changes in the flanking areas or (2) "successive contrast" stimuli in which the line itself changed in luminance. Line widths that gave optimal responses and response magnitudes themselves were similar for the two types of stimulus, except for the widest lines used (2 degrees). Thus, simultaneous brightness contrast is a primary determinant of the response of primate LGN cells but only within 2 degrees of the center of the receptive field. Neural processing up to this level cannot therefore explain the long distance effects of simultaneous brightness contrast in human perception.

The degree to which the sensation magnitude of a vibrotactile stimulus is enhanced by a prior stimulus was studied for vibration of the thenar eminence of the right hand. Enhancement was measured by a psychophysical matching procedure in which two brief stimuli separated by a variable time interval were presented to the skin and the subject adjusted a third stimulus to match the sensation magnitude of the second stimulus. By this procedure, it is possible to determine functional relationships between enhancement and the time interval between stimuli, the intensity of the stimuli, and the frequency of the stimuli. The results were consistent with the duplex model of mechanoreception.

The spatial tuning of macaque lateral geniculate neurones was compared for luminance-based and color-based lines. Lines of various widths were flashed on and centered on the cell's receptive field, and the size of the increase or decrease in firing was noted. Luminance-based lines consisted of 0.7 log unit increments or decrements. Color-based lines consisted of shifts in wavelength with no change in luminance, e.g., from a red field to a green line on a red field. The cell fired most to intermediate widths of luminance-based lines, but to the widest pure-color lines.

Human subjects rated the perceived intensity and pleasantness of taste mixtures (sucrose-quinine) and odor mixtures (lemon-heptanal or pyridine-lavender). The components of the mixture were judged as less intense when mixed than when judged alone. A multiple regression indicated that the pleasantness of a mixture can be predicted from a weighted additive function of the pleasantness values of the component sensations. Pleasantness values of the componetns had to be estimated from their pleasantness-intensity functions, because the perceived intensities of the components change when the components are combined. Weighting coefficients for the linear regressions were greater for the unpleasant components, especially in the odor mixtures.

Observers evaluated five odors and their 26 mixtures (two, three, four, and five components) by magnitude estimation. Estimates revealed that in mixtures there is moderate suppression of perceived intensity; a vector model proposed by Berglund (Annals of the New York Academy of Sciences, 1974, 237, 35-51) provides a good prediction of the intensity of binary mixtures, but overpredicts the intensity of three, four, and five component mixtures. Hedonic tones of mixtures were difficult to predict from hedonic tones of components. Qualities of mixtures were difficult to predict from quality of components. Intermediacy, of quality and hedonic values, was often observed.

A new and powerful procedure for determining frequency analysis in the auditory system, as evidence by the critical band, is described. The onset time difference, delta T, needed to lateralize 30-msec tone bursts toward the leading ear was measured as a function of the frequency difference, delta F, between the brust in one ear and the burst in the other ear. When delta F was less than the critical band, threshold delta T was constant at 100 mu sec or less, depending on center frequency; beyond the critical band, delta T increased with delta F. These dichotically measured critical bandwidths increased from 110 Hz at a center frequency of 500 Hz to 1100 Hz at a center frequency of 6000 Hz. They were unaffected by varying signal level from 25 to 80 dB or signal duration from 10 to 300 msec. The sam e critical-band values have been measured with monaural stimuli in loudness summation, maskin, detection, phase perception, consonance, and so forth.

An attempt to apply linear systems methods to the temporal properties of the human taste system is described. The percentage modulation in concentration required to detect a fluctuation in intensity was measured as a function of frequency of modulation. Both a sine-wave and a square-wave input were used. The sensitivity of the taste system at its maximum, and also at the low frequencies, was greater than expected from previous work based on classical methodology. The sensitivity of the taste system at its maximum, and also at the low frequencies, was greater then expected from previous work base on classical methodology. The sensitivity of the taste system to the various qualities was, in decreasing order, salty, sweet, sour, and bitter. The taste system in insensitive to frequencies above about 5 Hz. Except for bitter, representatives of the various taste qualities yielded similar functions within qualities.

The extent of cutaneous saltation (the illusory displacement of a tap presented to one skin locus by another tap occurring close in time at another locus) was modified by a "preconditioning" stimulus presented prior to and at a site distant from the saltatory test pattern. The 10-sec vibratory preconditioning (PC) stimulus appears to be analogous to inspection figures that "satiate" the perceptual field in experiments on figural aftereffects, producing changes in the perceived size, position, or shape of subsequent stimuli. The direction of displacement of the saltatory phantom was always away from the locus of the prior PC stimulus, consistent with results observed in studies of visual and kinesthetic aftereffects. Th- amount of repulsion and the rate at which the saltatory phantom returned to its initial position depend on the intensity, locus, and number of PC stimuli. As with figural aftereffects, these results resist explanation by peripheral mechanisms such as adaptation.

The excitability of the rat chorda tympani nerve following adaptation to NaCl was measured by observing the recovery of the transient portion of the integrated neural response. When a single concentration of NaCl was used as a test stimulus, recovery time was positively correlated with the concentration of the adapting solution, a relationship common to a number of other sensory systems. Adapting and testing with the same concentration of NaCl produced very little relationship between concentration and recovery time. It is suggested that the relativley extensive period of postexcitatory depression is due to a prolonged inaccessability of tast receptor sites that results in a reduction in the rate of stimulus-receptor interaction.

The phenomena of enhancement and suppression of vibrotactile subjective magnitude were investigated using a matching procedure. Results support earlier reports for audition and vibrotaction suggesting that enhancement is a fundamental sensory process. The time course is described for suppression of stimuli delivered to several different to several different pats of the body. The results are consistent with earlier studies of vibrotactile masking at threshold levels.