Adaptation of suprathreshold contrast and luminance stimuli

The temporal and spatial properties of the difference in perceived contrast and brightness of two suprathreshold stimuli presented successively in different retinal locations were determined. Stimulus onset asynchrony (SOA) was varied and the perceived contrast or brightness of the first stimulus (S1) was measured as a function of SOA by matching the contrast or luminance of the second stimulus (S2) to that of S1. The two stimuli overlapped in time for 200 ms to allow the comparison to be made. The adjusted values for S2 could well be fitted with an exponential decay function of SOA. For luminance increments and decrements the time constant for this function was 253 ms; for checkerboards with checks of size 16 min square the time constant was 164 ms. The difference in perceived contrast was dependent on initial contrast in a nonlinear fashion. It increased with increasing check size and was independent of the mean luminance and spatial proximity of the two stimuli. The phenomenon was observed with different pattern types and with dichoptic presentation, but could only be seen when direct comparison of the two stimuli was possible.     

Binocular interactions in suprathreshold contrast perception

Suprathreshold binocular contrast interactions were studied psychophysically. A split-screen CRT display was used to present separate sine-wave gratings to the observer’s left and right eyes. The method of constant stimuli and a modified method of adjustment were used to find sets of binoculartest patterns that matched a given binocularstandard. Test patterns consisted of the simultaneous presentation of sine-wave gratings that differed in contrast to the left and right eyes. Standard patterns consisted of identical sine-wave gratings presented to the two eyes, and had the same spatial frequency as the test patterns. Binocular contrast matching functions were obtained for several standard contrasts at 1 and 8 c/deg. Binocular matching functions were obtained for luminance increments as well. The binocular contrast matching functions departed from a simple binocular averaging rule, and behaved as if the eye receiving the higher contrast disproportionately dominated the binocular contrast percept. Departures from the binocular averaging rule were slightly greater for higher standard contrasts. Spatial frequency had little effect, and the luminance increment matching functions also departed from the binocular averaging rule. There was evidence for a contrast version of Fechner’s paradox and for substantial individual differences in a form of ocular dominance. In a further experiment, additivity of suprathreshold binocular contrast summation was examined by testing the double-cancellation condition. We found no systematic violations of additivity at 1 and 8 c/deg. Models of suprathreshold binocular contrast summation were examined.     

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.     

Apparent contrast of suprathreshold gratings varies with stimulus orientation

Human contrast sensitivity is known to vary with both stimulus spatial frequency and orientation. Previous research has indicated, however, that the apparent contrast of a sinusoidal grating is independent of spatial frequency at suprathreshold levels. We have found that the apparent contrast of suprathreshold gratings is not independent of its orientation. Observers adjusted the apparent contrasts of vertical and oblique gratings to match a 40% standard. Contrast match deviations were found at a number of spatial frequencies, indicating a lack of contrast constancy with stimulus orientation. The apparent contrast of gratings in different orientations could not be predicted in any simple fashion from either contrast threshold differences or ratios.     

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.     

Comparison of vibrotactile threshold and suprathreshold responses in men and women

Vibrotactile tb:resholds were measured on the thenar eminence of 12 men and 12 women at 10 sinusoidal frequencies. No significant differences between the two groups were observed. Magnitude estimation and production procedures carried out with 6 men and 6 women from the same groups showed that women perceive suprathreshold vibration stimuli as more intense than do men, although women and men do not differ in their estimation of the length of lines.     

Temporal summation and reaction time to double-light pulses at suprathreshold levels

Temporal summation of the visual system was studied at suprathreshold levels by measuring reaction time (RT) to the double pulses that were equal in luminance (L) and duration. The RTs were determined as functions of L and the stimulus onset asynchrony (SOA) between the onsets of the two pulses. The relation between RT and L obtained for a given SOA was found to be a power function with the exponent 1/3. The function relating L to SOA was then derived for each of three criterion RTs. The L-SOA relationship indicated partial summation at SOAs shorter than about 20 msec. Inhibition was observed at SOAs longer than about 80 msec. These findings were consistent with the predictions from a temporal integration model.     

Temperature and ph effects on the relative sweetness of suprathreshold mixtures of dextrose fructose

Increasing the temperature from 5 deg to 50 deg C did not significantly alter the relative sweetness of aqueous solutions of dextrose, fructose, and their combination, as measured by the method of magnitude estimation, with a panel of 12 experienced Ss. Reducing pH from 5.8 to 2.7 caused about a 50% reduction in relative sweetness for all stimuli tested. The slopes of these lines tended to decrease slightly, whereas the Y-intercept values showed the greatest change. In all experiments the slopes of the lines were reasonably stable, averaging 1.40 vs 1.3 reported by Stevens (1961) for sucrose. The results of these experiments are discussed in relation to previously reported data on taste interactions.     

The language of pain

The expression ‘pain’ refers to a phenomenon intrinsic to individuals. The object of the language of pain is restricted to an individual experience which excludes any form of direct access by others. Speaking about pain is thus one of the most difficult forms of linguistic activities, as has been repeatedly pointed out by Wittgenstein. The difficulties involved in this type of communication are not only dependent upon individual linguistic ability but are also clearly reflected in the state and structure of the linguistic means which are at the disposal of the speakers of a language. Linguistic means vary in status and complexity with respect to the ends which they can be used for. In this paper, I discuss two aspects of communicating pain: types of expression which are involved in speaking about pain, and linguistic activities which are carried out when speaking about pain. The two aspects are interrelated. My analysis makes use of categories belonging to the theory of linguistic activity and to the extended field theory of language (an expansion of Bühler's concept of symbolic and deictic field analysis of language).     

Use of verbal pain measurement in the detection of hidden psychological morbidity among low back pain patients with objective organic findings

Abstract

Patients with positive physical findings to explain low back pain arc believed lo belong to two organic subgroups. One group has organic disease alone: in the other, organic disease is accompanied by psychological disturbance. Separation of patients with medical findings into groups with varying levels of psychological disturbance is difficult, because emotional disturbance is often hidden. In this study, the pain report of 124 patients with organic findings alone, and 50 patients with organic and psychological findings was examined to determine whether pain measurement could he used to identify accurately patients belonging 10 the two groups. the pain groups differed in the use of 43 pain words from the Low Back Pain Symptom Check List. Using a set of weights derived From discriminant analysis. the 33 pain words predicted 99.2% of the patients with organic disease alone and 86.0% of the patients with organic disease and psychological disturbance. The results were replicated in a new sample of 140 patients. Cross-validation shrinkage in accuracy was 8.3%. The results of the two studies suggest that pain measurement may he a useful clinical indicator of psychological disturbance in patients with organic findings.     

The measurement of mood

Due to unfortunate choices of response scale and psychometric model earlier analyses of mood adjective check lists have given a confused and complex picture of the area. When an adequate response scale was applied and a simplex rather than a common factor analysis model was utilized it was found, in two empirical studies, that mood was possible to describe with a few bipolar factors. A theory is suggested where mood is seen as basically two-dimensional: one dimension being activity and the other pleasantness. More or less specific definitions of the content of experience with reference to the situation may then be used to define further dimensions, such as social orientation.