Perception of the form of stimulus increment as a method in assessment of the psychophysical relationship.

Among numerous procedures for determination of the psychophysical relation, one approach has seldom been applied. Essential in this method is to present a set of stimuli whose intensity increases in fixed time following different forms. The objective stimulus increment, which the subjects perceive as linear growth directly, represents the inverse psychophysical relation. In this paper the method was tested in the fields of click frequency and sound pressure. This procedure was named "Perception of the Form of Stimulus Increment in Time". In comparison to other psychophysical approaches, this one has several advantages. The principal ones are the following: (1) In assessing the psychophysical relation it is not necessary to try to measure the perceptual magnitude; and (2) the psychophysical relation is directly determined by its dynamic pattern. In this paper modifications to the method are reported which facilitate the subject's task and avoid some differences in subjects' individual approaches to the task. The modified procedure leads to results satisfactory independent of the influence of the factors irrelevant to the psychophysical relationship.

Influence of the intensity of NaCl solutions on adaptation degree and recovery time course.

The degree of adaptation and the time course of recovery after adaptation to NaCl solutions of various intensities were examined by magnitude estimation and simple sensory reaction time using a test stimulus of constant intensity. The results show that the degree of adaptation increased with the adapting concentration following a negatively accelerated function. Similarly, all recovery curves were negatively accelerated functions of the recovery time. The relation between the recovery constant (time necessary to attain two-thirds of normal responsivity) and adapting concentration approximates with both criteria more or less a linear function. Thus the recovery constant is a positively accelerated function of the degree of adaptation. The relationship between concentration and degree of adaptation can be approximated by Beidler's equation of taste stimulation, while the time course of recovery can be expressed by an exponential equation that can also be related to Beidler's theory. The two criteria used showed similar deteriorating effects of taste adaptation, indicating that reaction time can also be a useful criterion of the level of sensory responsivity.

Central processes in gustatory adaptation.

In two experiments the adapting stimuli at the periphery of the taste system were of a constant objective intensity but, using mixture suppression and spatial summation, their perceived intensity was varied. The results have shown that, in spite of the constancy in stimulus concentration, the adaptation degree changed with the perceived intensity of the stimulus. The adaptation to the compounds when in binary mixtures proved to be significantly less effective than the adaptation to the same equimolar compounds when unmixed. Similarly, the adaptation effects of solutions of a constant concentration, when applied to a small tongue area, were significantly smaller than when applied to a larger area. This adaptation dependence upon the taste sensation intensity suggests that in the gustatory adaptation, peripheral as well as central processes take part.

Interaction between stimuli with different taste qualities evaluated by reaction time.

The influence of adaptation to taste stimuli of 1 quality on tastants with other qualities was investigated by comparing the reaction time (RT) to a test solution after adapting-solution flow with the RT to the same test solution after water flow. Adapting solutions were strong concentrations of NaCl, HCl, QHCl, and sucrose; test solutions were the same compounds but in lower concentrations. Adaptation to sucrose significantly shortened RT to NaCl and HCl, and to a lesser degree to QHCl. A similar cross-enhancement was found in sucrose when other compounds served as adapting solutions, In all other taste combinations, only a cross-adaptation effect was observed. Results are discussed in relation to some adaptation phenomena, water taste data, and magnitude-estimation data.

Time course of recovery from gustatory adaptation to NaCl.

Recovery from adaptation to NaCl was tested by comparing some relevant parameters of response to the adapting and test stimuli separated by different recovery intervals. The time course of response was determined using magnitude estimations and using the flow chamber for stimulus delivery. The course of recovery for all parameters used was a negatively accelerated function of the rest time, but the recovery rate of different parameters did not prove to be equal. Recovery was fastest for the initial maximum taste magnitude, followed by the time needed for the taste to disappear. The taste effect summed over time and the time required for the taste magnitude to decrease to 30% of its preadapted maximum were the slowest to recover. Although the recovery processes proceeded at a rapid rate during the initial period, all parameters remained depressed over a rather long period.

Magnitude estimation of adaptation to salt using a flow chamber for stimulus delivery.

Adaptation course to NaCl was estimated using a flow chamber for stimulus delivery and changes in the perceived taste magnitude as the criterion. The adapting stimulus of different durations was applied to one side of the tongue. Magnitude estimates were made by comparing the intensity of taste at the end of each adaptation time with the perceived intensity of the same stimulus applied briefly to the unadapted side of the tongue. The course of adaptation followed a negatively accelerated decreasing function. The relationship between taste magnitude and the duration of the adapting stimulus can be approximated by a logarithmic equation and, somewhat less accurately, also by an exponential equation, which can be related to the Beidler theory of taste stimulation. Some advantages of the closed flow technique and comparison of taste magnitudes on the adapted and unadapted sides of the tongue are discussed.

Individual gustatory reaction times to various groups of chemicals that provoke basic taste qualities.

Reaction times (RTs) to four groups of substances that provoke different taste qualities were measured. Measurements for all substances with the same taste, equalized in perceived intensity and provoking a very strong taste, were made concurrently for each subject. The comparisons were made on the individual level. No significant differences in RTs to substances with the same taste quality were found. When the factor of perceived intensity is kept constant, no effect of the stimulus chemical composition on RTs seems to be present. RTs to stimuli with different tastes differ significantly, the shortest being to salt and the longest to bitter. The difference in RTs for sour and sweet substances is small, and the subjects were not all alike in terms of the order of RTs with respect to these stimuli.