Olfactory adaptation and recovery in man as measured by two psychophysical techniques

Olfactory adaptation and recovery was investigated in man, using two psychophysical procedures: modified category scaling and threshold detection. Both procedures yielded similar qualitative information regarding loss and recovery of olfactory sensitivity as a function of time and concentration of adapting stimuli. However, quantitative differences were observed that could be partially attributed to artifacts inherent in each procedure. Often more than 50% adaptation (and recovery) occurred within the first 2 min with either test procedure. In all experiments the rate of adaptation and recovery was greater at the higher of two adapting concentrations (10 × and 20 × the detection threshold I_t). Recovery occurred more rapidly than adaptation. The usefulness of both techniques is discussed in terms of the overall problem of characterizing the olfactory adaptation and recovery process in man.     

Differential luminance sensitivity of the human visual system

In this paper the differential sensitivity of the visual system is investigated by means of two simultaneously presented stimuli in a yes-no procedure. The sensitivity measure σ_I appears to be proportional to stimulus intensity (i.e., Weber’s law). The curve displaying Weber’s law is little affected by variation of the background intensity or of the adaptation level. An increment threshold experiment using only one stimulus yields a proportionality of σ_I with the square root of the background intensity. An additional experiment shows that the sensitivity measure σ_I for two flashes decreases first, from dark up to a particular background intensity, and increases when the background tends to mask the flashes. So, in general, two background levels exist with the same differential sensitivity. The results cannot easily be explained by the simple quantum fluctuation concept. A model based partially on electrophysiological data from the literature is proposed which encounters a particular adaptation mechanism, a transducer with a limited dynamical range, and a range setting mechanism.     

Vibrotactile threshold shift during magnitude-estimation scaling on the hand: effects on magnitude-estimation responses and scaling behavior

The purpose of the present study was to determine whether threshold shifts occurred during magnitude-estimation scaling of suprathreshold stimuli presented to the thenar eminence of the right hand. Possible relationships of the vibrotactile threshold shifts to suprathreshold stimulus intensity, magnitude-estimation responses, and over-all scaling behavior were explored. A single group of 14 subjects whose ages ranged from 18 to 22 yr. participated. Each subject performed two magnitude-estimation tasks. In one of the tasks threshold of sensitivity was determined after every suprathreshold numerical response of the subject. If a threshold shift was recorded, threshold was allowed to return to pretest baseline level before continuation to the next suprathreshold stimulus presentation. Analysis showed that threshold shift did occur during vibrotactile magnitude-estimation scaling on the hand and that it was related to suprathreshold stimulus intensity. Results also showed that the subjects' numerical magnitude-estimation responses and over-all scaling behavior in the form of power function exponents were not statistically different for the two scaling tasks.     

Sensation magnitude of vibrotactile stimuli

A systematic investigation of the subjective magnitude of vibrotaction was undertaken to: (1) determine the growth of sensation as a function of stimulus intensity; (2) establish contours of equal subjective magnitude; and (3) compare over a wide range of frequency and intensity the psychophysical methods of direct scaling and intensity matching. The results show that the data obtained by direct scaling are comparable to the data obtained by interfrequency matching. The subjective magnitude function is a power function with a slope of about 0.89 for frequencies up to 350 Hz. Near threshold the growth of sensation is proportional to the physical intensity. Contours of equal subjective magnitude for vibration across 10 frequencies and at 11 levels of intensity are given.     

Odor intensity after self-adaptation and cross-adaptation

Psychophysical functions for the odor intensity of n-propanol and n-pentanol were obtained after no adaptation and after self-adaptation and cross-adaptation. Adaptation caused the psychophysical function to become steeper and generally concave downward in log-log coordinates. Increase in the in tensity of a: self-adapting stimulus produced relatively greater increases in the steepness of the functions than did increases in adapting duration. A comparison between the odorants revealed that propanol and pentanol have equal self-adapting effects when their respective adapting concentrations are matched for subjective intensity. Cross-adaptation had approximately the same effect as self-adaptation on the form of the psychophysical function, but a cross-adapting stimulus of a specified subjective intensity was less effective than a self-adapting stimulus of the same intensity. Adaptation to pentanol caused a larger reduction in the perceived intensity of propanol than adaptation to propanol caused in the perceived intensity of pentanol.     

Lingual vibrotactile/auditory magnitude estimation and cross-modal matching: comparison of suprathreshold responses in men and women

The purpose of this study was to investigate the response patterns of men and women to suprathreshold lingual-vibrotactile and auditory stimulation. The psychophysical methods of magnitude estimation and cross-modal matching were used on a group of 10 men (M age = 19.6 yr.) and 10 women (M age = 20.2 yr.). Analysis showed that the men and women performed differently on the magnitude-estimation tasks and similarly on the cross-modal matching tasks. These results suggested that sex differences on suprathreshold psychophysical scaling may be related to the way men and women use numbers as opposed to possible differences in the perception of suprathreshold sensory stimuli by men and women.     

Lingual vibrotactile threshold shift differences between stutterers and normal speakers during magnitude-estimation scaling

The purpose of this study was to investigate differences in tactile sensory system function between stutterers and normal speakers. This task was accomplished by studying possible tactile threshold shifts occurring during magnitude-estimation scaling of vibratory stimuli presented to the dorsal surface of the tongue. Ten normal speaking men (M age = 19.7 yr.) and 10 stutterers (M age = 25.9 yr.) participated. Analysis suggested that stutterers and normal speakers differ in terms of the responsiveness of the sensory mechanism for the lingual tactile threshold to vibratory stimulus intensities applied at suprathreshold levels. The stutterers and normal speakers performed similarly on all aspects of the magnitude-estimation scaling tasks, but the amount of threshold shift occurring during the scaling procedures was significantly greater for the stutterers at each suprathreshold intensity level employed.     

The nature and duration of adaptation following long-term odor exposure

Any individual living or working in an odorous environment can experience changes in odor perception, some of which are long lasting. Often, these individuals report a significant reduction in the perception of an odor following long-term exposure to that odor (adaptation). Yet, most experimental analyses of olfactory adaptation use brief odorant exposures which may not typify real-world experiences. Using a procedure combining long-term odor exposure in a naturalistic setting with psychophysical tests in the laboratory, we present evidence to show that reduced odor intensity following long-term exposure is accompanied by odorant-specific shifts in threshold. Subjects were exposed continuously to one of two odorants while in their home for a period of 2 weeks. Exposure produced an odorant-specific reduction in sensitivity and perceived intensity compared with preexposure baselines: Detection thresholds for the adapting odorant were elevated following exposure and perceived intensity ratings for weak concentrations were reduced. For most individuals, reduced sensitivity to the test odorant was still evident up to 2 weeks following the last exposure. The persistence of the change, as evidenced by the duration of recovery from adaptation, distinguishes this phenomenon from the adaptation seen following shorter exposures and highlights the need for the study of exposure durations that are more similar to real-world exposures.     

Nonlocal determination of brightness in spatially periodic patterns

Recent data require nonlinear spatial summation processes in models for detection of spatially periodic and aperiodic patterns. Contrast matching experiments with suprathreshold grating and spot patterns suggest that nonlinear models may be required for suprathreshold contrast data, but differences between the psychophysical tasks used with periodic and aperiodic patterns make comparison difficult. A series of experiments are reported in which subjects matched local brightnesses and brightness differences within single cycles of grating patterns. This task closely resembles the matching task in classical contrast experiments with aperiodic stimuli, allowing comparison of the data from the two types of experiments. Brightnesses within a 5-cycle/degree (c/deg) sinusoidal grating were largely unaffected by addition of a large 15-c/deg modulation component in either of two phases, in spite of the resulting large change in local luminances within the pattern. As at threshold, complex models are required in order to account for apparent differences between spatial interactions within periodic and aperiodic patterns.     

A comparison of olfactory adaptation among seven odorants and their relationship with several physicochemical properties

A study was made comparing olfactory sensitivity before and after 100 sec of adaptation for stimuli representing several odorant classes with varying physicochemical properties. Measures taken were absolute detection thresholds and magnitude estimates of suprathreshold stimuli. Significant rank-order correlation coefficients (<.90) were found between nonadapted and adapted absolute detection thresholds, vapor pressure, and percent adaptation.     

Threshold tracking for assessment of long-term adaptation and sensitization in pain perception

To assess temporal variations in the perception of "phasic" heat pain stimuli a psychophysical tracking procedure was developed that enables repeated assessment of the pain threshold at short intervals. This "double-tracking" procedure produces two tracking curves simultaneously, one that approaches the pain threshold gradually from above, the other from below. The threshold for phasic heat pain was measured in 80 tracking trials with stimuli at temperatures near the pain threshold. Concurrently, the threshold for "tonic" heat pain was determined after every 20 tracking trials with a stimulus adjustment procedure. Eleven healthy subjects (age: 26.4 yr. +/- 6.0) participated in 2 sessions each. Phasic stimulation near the pain threshold did not produce any trends in either of the two threshold measures. Hence there was no long-term adaptation or sensitization. However, there were random variations (random walks) in the tracking curves, which we interpret as resulting from a stochastic relationship between stimulus and sensation. In agreement with other reports, discrimination seemed to be better at painful than at nonpainful temperatures.     

Vibrotactile temporal summation for threshold and suprathreshold levels of stimulation

Threshold measurement and matching procedures were used to determine the amount of temporal summation at threshold and suprathreshold levels of vibrotactile stimulation on the thenar eminence of the hand. The frequency of the stimulus was 25, 40, 80, or 200 Hz. At 25 Hz, temporal summation was absent at all intensity levels. Considerable amounts of temporal summation were observed for 80- and 200-Hz stimuli, although the effects decreased as a function of intensity. At 40 Hz, no temporal summation was observed at threshold, but above threshold, a small amount was observed at all intensity levels. The results support a duplex model of mechanoreception in which one of two receptor systems exhibits temporal summation.     

Intensity resolution and subjective magnitude in psychophysical scaling

Several successful theories of psychophysical judgment imply that exponents of power functions in scaling tasks should covary with measures of intensity resolution such asd’ in the same tasks, whereas the prevailing metatheory of ideal psychophysical scaling asserts the independence of the two. In a direct test of this relationship, three prominent psychophysical scaling paradigms were studied: category judgment without an identification function, absolute magnitude estimation, and cross-modality matching with light intensity as the response continuum. Separate groups of subjects for each scaling paradigm made repeated judgments of the loudnesses of the pure tones that constituted each of two stimulus ensembles. The narrow- and wide-range ensembles shared six identical stimulus intensities in the middle of each set. Intensity resolution, as measured byd’-like distances, of these physically identical stimuli was significantly worse for the wide-range set for all three methods. Exponents of power functions fitted to geometric mean responses, and in magnitude estimation and cross-modality matching the geometric mean responses themselves, were also significantly smaller in the wide-range condition. The variation of power function exponents, and of psychophysical scale values, for stimulus intensities that were identical in the two stimulus sets with the intensities of other members of the ensembles is inconsistent with the metatheory on which modern psychophysical scaling practice is based, although it is consistent with other useful approaches to measurement of psychological magnitudes.     

Thresholds for detection and awareness of masked facial stimuli

It has been suggested that perception without awareness can be demonstrated by a dissociation between performance in objective (forced-choice) and subjective (yes–no) tasks, and such dissociations have been reported both for simple stimuli and more complex ones including faces. However, signal detection theory (SDT) indicates that the subjective measures used to assess awareness in such studies can be affected by response bias, which could account for the observed dissociation, and this was confirmed by Balsdon and Azzopardi (2015) using simple visual targets. However, this finding may not apply to all types of stimulus, as the detectability of complex targets such as faces is known to be affected by their configuration as well as by their stimulus energy. We tested this with a comparison of forced-choice and yes–no detection of facial stimuli depicting happy or angry or fearful expressions using a backward masking paradigm, and using SDT methods including correcting for unequal variances in the underlying signal distributions, to measure sensitivity independently of response criterion in 12 normal observers. In 47 out 48 comparisons there was no significant difference between sensitivity (d_a) in the two tasks: hence, across the range of expressions tested it appears that the configuration of complex stimuli does not enhance detectability independently of awareness. The results imply that, on the basis of psychophysical experiments in normal observers, there is no reason to postulate that performance and awareness are mediated by separate processes.     

Effects of aging on the suprathreshold responses to vibration

The psychophysical responses to vibration of two age groups (22 or 25 and 66 years) were compared for two tasks using suprathreshold levels of vibrotactile stimulation. At a vibration frequency of 25 Hz, the two age groups gave similar curves of subjective magnitude determined by the method of absolute magnitude estimation. At 250 Hz, the curve of the older group showed no recruitment over low levels of intensity. Instead, their magnitude estimates were depressed over the entire range of intensities. Sensory persistence, measured by a matching procedure, was more marked in the older group.     

Lingual vibrotactile threshold shift during magnitude-estimation scaling: effects on magnitude-estimation responses and scaling behavior

The purpose of the present study was to determine if lingual vibrotactile threshold shifts occurred during magnitude-estimation scaling of suprathreshold stimuli presented to the dorsal surface of the tongue. Possible relationships of the lingual vibrotactile threshold shifts to suprathreshold stimulus intensity, magnitude-estimation responses, and overall scaling behavior were explored. A single group of 24 subjects with an age range of 18 to 22 years participated in this study. Each subject performed two magnitude-estimation tasks. In one of the tasks, threshold of sensitivity was determined after every suprathreshold numerical response of the subject. If a threshold shift was recorded, threshold was allowed to return to the pretest baseline level before continuing to the next suprathreshold stimulus presentation. The results showed that threshold shift did occur during lingual vibrotactile magnitude-estimation scaling, and that it was related to suprathreshold stimulus intensity. The results also showed that the numerical magnitude-estimation responses of the subjects were different for the two scaling tasks. Overall scaling behavior of the subjects in the form of power-function exponents was not different for the two tasks.     

Ipsi-and bilateral interactions in taste

In two experiments, the integration over spatial extent in taste was investigated for threshold sensitivity to NaCl and for suprathreshold intensity perception of saltiness. The area of stimulation was doubled by adding either an ipsilateral or a bilateral stimulus. The two stimuli could be of equal or unequal intensity. The data showed that at threshold level a probability summation model applied to all bilateral and most of the ipsilateral stimulus combinations. Probability summation failed to predict detection probability when two stimuli with different intensities were presented at the same tongue side. For suprathreshold stimuli, the magnitude of the saltiness sensation as estimated by a line-length method depended on the level of stimulation. The possible peripheral interaction mechanisms and central factors contributing to the taste response were discussed.     

Informational and neural adaptation curves are asynchronous.

Norwich's entropy theory of perception (plus a few additional assumptions) suggests the existence of an "infromational adaptation curves" (change in stimulus equivocation with stimulus duration) for suprathreshold prothetic stimuli that is synchronous with the "neural adaptation curve" (change in firing rate with stimulus duration) observed for sensory neurons. Five experiments are reported in which informational adaptation curves were measured for auditory and visual stimuli by having subjects make absolute identifications of suprathreshold sound or light intenstiies of various durations. Information transmissions for the shortest duration stimuli (1 and 5 msec, respectively, for light and sound) were surprisingly large (small equivocations), indicating that intensity information is acquired very rapidly by the whole organism. The equations of entropy theory were fitted to adaptation data for peripheral sensory neurons (spiral ganglion cells and retinal ganglion cells) and were compared to the informational adaptation curves. It was found that informational adaptation occurred more rapidly than neural adaptation. That is, the two types of adaptation process are asynchronous. However, for both audition and vision, the total amount of information mediated by the adaptation process (channel capacity) was about the same for both types of processes (2.03 bits vs. 2.1 bits per stimulus for sound intensity; 1.3 vs. 2.0 bits per stimulus for light intensity). Faster acquisition could be accomplished in the whole organism through convergent neural circuits that increase sampling rate by pooling the samples taken by individual receptor systems.     

Evoked potentials and sensation

Objective physiological measurements (evoked potentials) were compared with the corresponding psychophysical observations for human Ss. Discrepancies were found between the amplitude of the steady-state evoked potential (EP) and the sensations of flicker produced by visual stimuli of different modulation depths. Poor correlations were also found between subjective De Lange curves and amplitude vs frequency curves for the EP under conditions of chromatic adaptation. It is suggested that two classes of EP can be distinguished; one correlates well and the other correlates poorly with sensation.     

Neural representation of consciously imperceptible speech sound differences

The concept of subliminal perception has been a subject of interest and controversy for decades. Of interest in the present investigation was whether a neurophysiologic index of stimulus change could be elicited to speech sound contrasts that were consciously indiscriminable. The stimuli were chosen on the basis of each individual subject's discrimination threshold. The speech stimuli (which varied along an F3 onset frequency continuum from /da/ to /ga/) were synthesized so that the acoustical properties of the stimuli could be tightly controlled. Subthreshold and suprathreshold stimuli were chosen on the basis of behavioral ability demonstrated during psychophysical testing. A significant neural representation of stimulus change, reflected by the mismatch negativity response, was obtained in all but 1 subject in response to subthreshold stimuli. Grand average responses differed significantly from responses obtained in a control condition consisting of physiologic responses elicited by physically identical stimuli. Furthermore, responses to suprathreshold stimuli (close to threshold) did not differ significantly from subthreshold responses with respect to latency, amplitude, or area. These results suggest that neural representation of consciously imperceptible stimulus differences occurs and that this representation occurs at a preattentive level.