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At least 109 records · Page 6Linked to original sources
PubMed2004

Psychophysical sensory examination in individuals with a history of methylmercury exposure.

Paresthesias are the first symptom that people report following toxic doses of methylmercury. The authors conducted a psychophysical study of tactile sensation to evaluate the somatosensory abilities of subjects living in a methylmercury-polluted area around Minamata City, Japan. The authors examined control subjects and methylmercury-exposed subjects with and without numbness. A history of methylmercury exposure was taken and a neurological examination performed. Aluminum-oxide abrasive papers were used as stimuli in a psychophysical sensory examination of fine-surface-texture discrimination. Difference thresholds from 3 microm were calculated by the two-alternative, forced-choice technique. Difference thresholds in control subjects were also calculated for comparison. The difference threshold was 6.3 microm in exposed subjects with sensory symptoms, 4.9 microm in exposed subjects without sensory symptoms, and 2.7 microm in control subjects. Acuity of fine-surface-texture discrimination was disturbed not only in subjects with clinical complaints of hand numbness, but also in subjects without hand numbness who lived in the district where methylmercury exposure occurred. Sensory testing using a psychophysical test of fine-surface-texture discrimination in this population suggests that the number of individuals affected by methylmercury exposure in the polluted area was greater than previously reported.

Aged↗
PubMed1997

Electroretinographic and psychophysical findings during early and late stages of human immunodeficiency virus infection and cytomegalovirus retinitis.

PURPOSE: The authors examined electrophysiologic and psychophysical measures of retinal function in patients infected with human immunodeficiency virus (HIV) at different stages of infection, including patients with cytomegalovirus retinitis (CMVR). METHODS: All patients had complete ophthalmologic examinations. Rod-mediated psychophysical thresholds were measured using a modified two-color dark-adapted perimetry technique. Rod-dominated full field flash electroretinograms (ERGs) were obtained as a function of flash intensity, followed by cone-dominated ERGs. The 26 patients infected with HIV (26 eyes) were categorized into three groups. Six patients were infected with HIV but had not progressed to acquired immunodeficiency syndrome (AIDS), and 14 had AIDS. Six patients had CMVR with less than 10% of the retina involved. The data were compared with results from age-similar control subjects. RESULTS: Psychophysical thresholds as a function of retinal eccentricity were elevated for each of the three stages of HIV infection. The group of patients with CMVR had the greatest amount of threshold elevation and threshold elevation increased with retinal eccentricity. In addition, all three patient groups had abnormal electroretinographic findings. Patients with CMVR were affected more severely on all measures than were the other HIV-infected groups. CONCLUSIONS: Results reveal that a diffuse functional retinal pathology exists in eyes with the funduscopic appearance of localized peripheral CMVR. Additionally, patients infected with HIV, including those without cotton wool spots, may have abnormal retinal function.

Adult↗
PubMed2003

Psychophysical threshold variability in cochlear implant subjects.

The dramatic differences observed when comparing auditory neural responses to electrical and acoustic stimulation may illustrate one of the important mechanisms underlying the sometimes poor speech recognition abilities of individuals with cochlear implants. Recent research has suggested that the absence of a stochastic component in neural responses to electrical activation may be an important potential mechanism for this degradation in speech recognition performance. There are few psychophysical data, however, demonstrating that this stochastic behavior can be measured directly in implant subjects. In this study, variability in psychophysical threshold was investigated as a measure of the stochastic nature of the underlying neural response in human and non-human subjects implanted with intracochlear electrode arrays. Threshold data collected in both monopolar and bipolar stimulation modes at several phase durations from cat and human subjects are presented. The nature of the neural input/output curve suggests that threshold variability should increase as the slope of the input/output curve is decreased, i.e. as phase duration is increased. These predictions are confirmed by the pattern of psychophysical results measured experimentally in cat and human subjects. Furthermore, the data may suggest that subjects with higher threshold variability, i.e. a relatively greater stochastic component, are more likely to have higher speech recognition scores.

Aged↗
PubMed1999

Across-species comparisons of psychophysical detection thresholds for electrical stimulation of the cochlea: II. Strength-duration functions for single, biphasic pulses.

This paper compares psychophysical detection threshold data (new and previously published) for pulsatile electrical stimulation of the deafened inner ear, obtained from different human and nonhuman subjects. Subjects were grouped according to species. Other variables, however, such as the electrode array type and method of deafening, varied within and across species. Detection threshold levels and slopes of threshold versus phase duration functions for presentations of single, biphasic pulsatile stimuli (strength-duration functions) were compared for humans, macaques, cats, and guinea pigs. For bipolar stimulation, statistically significant differences in threshold level were observed between human subjects and all other species. The species difference did not depend on the phase duration tested. For monopolar stimulation, only nonhuman species were tested. Effects of electrode configuration on both the level and slope of psychophysical strength-duration functions were statistically significant across nonhuman species, but there was not a statistically significant interaction between species and electrode configuration. The similarity in function shape and relative paucity of significant differences in psychophysical functions across species support the continued use of multiple species for cochlear implant research.

Animals↗
PubMed1996

Electrically evoked whole nerve action potentials in Ineraid cochlear implant users: responses to different stimulating electrode configurations and comparison to psychophysical responses.

Electrically evoked whole nerve action potentials (EAP) have been recorded from 20 ineraid cochlear implant users in response to bipolar and/or monopolar electrical stimulation of the cochlea. EAP growth functions and refractory recovery functions were obtained for a variety of different stimulating conditions. Where possible, parallel psychophysical experiments were conducted that measured the just detectable increment in stimulus current level (JND), forward-masking functions, and detection thresholds for a range of different stimuli. Variations in EAP threshold, slope of the EAP growth function, and the rate of recovery of the EAP from the refractory state were observed both across subjects for a given place and by mode of stimulation (bipolar versus monopolar), as well as across electrodes within a subject. A poor correlation between slope of the EAP growth functions and current JNDs was obtained. However, good correlations were observed between EAP threshold and psychophysical detection threshold and between the EAP refractory recovery functions and the psychophysical forward-masking functions. Our interpretation of these findings is that these particular physiological measures are related to the excitability of the auditory nerve to electrical stimulation and further that these measures are related to performance of cochlear implant patients on listening tasks. Consequently, such information may prove to be useful in adjusting the stimulation parameters of the cochlear implant speech processor in order to maximize an individual's performance with the device.

Cochlear Implants↗
PubMed1997

The psychophysics of J-R-L Delboeuf (1831-1896).

Delboeuf's writings on psychophysics are little known nowadays. The object of this paper is to describe the psychological contributions of this eminent Belgian psychologist of the second half of the 19th century. A true pioneer of experimental psychology, his work on psychophysics began in 1865 at the University of Gand (Ghent) but was not published until 1873 and following years. His work in this area is characterised on the one hand by the adoption of a logarithmic law relating sensation strength to stimulus strength, but which differed from that of Fechner; and on the other hand by the utilisation of a psychophysical technique based on brightness contrast (now called the 'bisection method'). Even though, Delboeuf was classified by Fechner in his later writings as an opponent of his beliefs. Delboeuf was nevertheless one of his least-virulent critics and the only psychologist of that era to have adopted a logarithmic law. Delboeuf's work is not only of historic interest; his original ideas possess sufficient interest for present-day psychophysicists to reexamine them.

Belgium↗
PubMed2004

The tale is in the tail: an alternative hypothesis for psychophysical performance variability in dyslexia.

Dyslexic groups have been reported to display poorer mean performance than groups of normal readers on a variety of psychophysical tasks. However, inspection of the distribution of individual scores for each group typically reveals that the majority of dyslexic observers actually perform within the normal range. Differences between group means often reflect the influence of a small number of dyslexic individuals who perform very poorly. While such findings are typically interpreted as evidence for specific perceptual deficiencies in dyslexia, caution in this approach is necessary. In this study we examined how general difficulties with task completion might manifest themselves in group psychophysical studies. Simulations of the effect of errant or inattentive trials on performance produced patterns of variability similar to those seen in dyslexic groups. Additionally, predicted relationships between the relative variability in dyslexic and control groups, and the magnitude of group differences bore close resemblance to the outcomes of a meta-analysis of empirical studies. These results suggest that general, nonsensory difficulties may underlie the poor performance of dyslexic groups on many psychophysical tasks. Implications and recommendations for future research are discussed.

Contrast Sensitivity↗
PubMed1978

The psychophysical relationships between color and flavor.

Psychophysics has become a well-defined discipline in science and is undergoing a period of transition from the theoretical and academic to the applied. Certainly the use of magnitude estimation in flavor evaluation is becoming more accepted, and concurrently the food research area is utilizing the colorimetric techniques which are available. However, there has been virtually no investigation carried out on the quantitative relationships which exist between color and flavor in a psychophysical sense. Intuitively, many researchers state the qualitative effect of color on flavor, but the quantification of these techniques is practically nonexistent. This paper will attempt to summarize the psychophysical techniques which are available for such studies, as well as discuss the importance of these studies. Great controversy exists concerning the need for colorants in food. If color does indeed affect flavor quantitatively, it will affect intake and, therefore, final nutritional status of the public in a quantitative manner. This controversy should be resolved in the light of fact, not intuition.

Color↗
PubMed1988

Effects of psychophysical lifting training on maximal repetitive lifting capacity.

The purpose of this investigation was to determine the effectiveness of psychophysical lifting training on maximal repetitive lifting capacity. Maximal repetitive lifting capacity was defined as the maximum box mass that could be lifted for 1 hr to a height of 132 cm at a rate of 6 lifts/min. Eight male subjects participated in five psychophysical lifting training sessions each week for 4 weeks. During each session subjects were presented with one empty and one heavily loaded box and asked to adjust the box mass to the maximum load they felt capable of lifting for 1 hr. This load was lifted at a rate of 6 lifts/min to a height of 132 cm for two 15-min periods each session. Heart rate was recorded, and subjects were asked to provide a rating of their perceived exertion. At the end of 4 weeks of training, subjects did not select a heavier training load, exhibit a decreased training heart rate, or report a decreased rating of perceived exertion. The training program did produce a significant increase in 1-hr maximal repetitive lifting capacity, as indicated by a greater box mass selected, but there was no concomitant change in VO2, heart rate, or rating of perceived exertion. It can be concluded that 4 weeks of psychophysical training of inexperienced lifters can produce a substantial increase in work output for a given energy expenditure. These increases are attributed to neural factors (skill, neuromuscular coordination) and to possible increases in the muscular endurance of specific muscle groups occurring with practice.

Adult↗
PubMed1994

A psychophysical study of the mechanisms of sensory recovery following nerve injury in humans.

Twenty-four subjects were studied before and up to 1 year after surgery that produced injury to a major sensory branch of the trigeminal nerve. We employed a battery of 11 psychophysical tests, in which the neural mechanisms underlying performance are understood, to study the basis of recovery following nerve injury. Immediately after nerve injury, sensation was profoundly impaired in all subjects. In the following weeks and months, the recovery of performance proceeded in an orderly fashion. Although the rates of recovery varied between subjects, the order of recovery between tasks did not. The recovery rates fell into three distinct categories. Recovery in one task, brush-stroke directional discrimination, was most rapid. Two weeks after nerve injury, 52% of subjects could discriminate brush-stroke direction; by 3 months only one subject could not perform this task. The second category comprised recovery rates for pain thresholds for noxious heat, cold and mechanical stimuli, and to preinjury performance in tasks assessing touch and vibration detection, two-point discrimination, cooling detection and subjective magnitude estimation of mechanical force. The third, slowest group included recovery rates for warming detection and grating orientation discrimination. Early recovery to preinjury performance levels in the brush-stroke direction and one-point versus two-point discrimination tasks was correlated with later recovery to near normal performance in the grating orientation task. The grating orientation task was unique in providing a measure that corresponded consistently with the subjects' reports of sensory deficits. Our psychophysical findings are consistent with neurophysiological data showing that the major primary afferent fibre classes reinnervate the skin at a similar rate. A hypothesis that accounts for the psychophysical findings in this study is that differences in recovery rates between tasks is determined largely by their relative dependencies on functional innervation density. Alternative hypotheses are considered.

Adolescent↗
PubMed2000

Correlation of MRI lesions with visual psychophysical deficit in secondary progressive multiple sclerosis.

The aim of this work was, first, to clarify the nature of the relationship between the sensory deficit in the demyelinated visual pathway and morphological changes revealed by MRI and, secondly, to test whether there was a preferential effect of demyelination for either the magnocellular or parvocellular pathway in established multiple sclerosis. Twenty-four patients with secondary progressive multiple sclerosis were studied psychophysically and by MRI of the optic nerve and brain. MRI was performed with a Phillips (0.5T) scanner. Visual pathway MRI lesion load was evaluated independently using the total optic nerve lesion length and lesion area seen on STIR (short inversion time inversion recovery) images of the optic nerve and the total post-chiasmal lesion area on T(1)-, T(2)- and proton-density-weighted images of the brain. Psychophysical tests determined 75%-seeing thresholds for horizontal gratings consisting of isoluminant red and green sinusoids of the same spatial frequency combined out-of-phase for preferential stimulation of the parvocellular system and in-phase for preferential stimulation of the magnocellular system. It was found that, in this group of patients, visual psychophysical loss was significantly correlated with lesion area seen on proton density MRI sequences of the post-chiasmal visual pathway, and that the parvocellular pathway was more affected than the magnocellular pathway, especially at lower spatial frequencies.

Adolescent↗
PubMed1999

Psychophysical laws revealed by electric hearing.

Psychophysical laws relate the intensity of a physical stimulus to its perceived magnitude. G.T. Fechner hypothesized 150 years ago that the psychophysical law can be derived by measuring intensity discrimination, but modern scientists favor a direct magnitude estimation approach and are still divided on whether and how intensity discrimination is related to sensation magnitude. This controversy is partially due to the uncertainty of the role of the sensory organ in the psychophysical law. Here we bypass the auditory sensory organ with electric stimulation of the human auditory nerve and find a close coupling between intensity discrimination and loudness functions in electric hearing. Our results support Fechner's hypothesis in principle but not the exact relationship from which he derived his logarithmic law.

Adult↗
PubMed1983

Psychophysical studies on the binocular processes of amblyopes.

It has frequently been assumed that humans with abnormal binocular vision resulting from amblyopia or strabismus lack binocular cortical neurons. From this assumption, it would be predicted that amblyopes would fail to show binocular interactions on any psychophysical tasks. This paper describes some recent psychophysical experiments investigating the binocular processes of amblyopes. The results of these experiments have shown that most humans with abnormal binocular vision fail to show binocular interactions for psychophysical tasks such as stereopsis or binocular summation, but show partially normal binocular interactions for interocular transfer of visual aftereffects and show normal interactions for dichoptic masking with grating stimuli.

Amblyopia↗
PubMed2006

Psychophysics of sweet and fat perception in obesity: problems, solutions and new perspectives.

Psychophysical comparisons seem to show that obese individuals experience normal sweet and fat sensations, they like sweetness the same or less, but like fat more than the non-obese do. These psychophysical comparisons have been made using scales (visual analogue or category) that assume intensity labels (e.g. extremely) which denote the same absolute perceived intensity to all. In reality, the perceived intensities denoted by labels vary because they depend on experiences with the substances to be judged. This variation makes comparisons invalid. Valid comparisons can be made by asking the subjects to rate their sensory/hedonic experiences in contexts that are not related to the specific experiences of interest. Using this methodology, we present the evidence that the sensory and hedonic properties of sweet and fat vary with body mass index. The obese live in different orosensory and orohedonic worlds than do the non-obese; the obese experience reduced sweetness, which probably intensifies fat sensations, and the obese like both sweet and fat more than the non-obese do. Genetic variation as well as taste pathology contribute to these results. These psychophysical advances will impact experimental as well as clinical studies of obesity and other eating disorders.

Dietary Fats↗
PubMed2004

Quantifying the auditory saltation illusion: an objective psychophysical methodology.

Under conditions of rapid presentation, brief acoustic stimuli repeatedly delivered first at one location, then at another, are systematically mislocalized, with stimuli perceived as traveling smoothly between the two locations. This robust illusory motion percept is termed "auditory saltation." Currently, the characteristics and mechanisms of auditory saltation are not well understood. The lack of objective methods capable of quantifying the illusion on an individual basis seems a limiting factor for this area of research. In this study, we outline an objective psychophysical task that estimates the interstimulus interval at which the saltation illusion is reliably distinguishable from simulated motion. Experiment 1 examined the psychophysical function relating task performance to ISI and addressed the suitability of the task for use with adaptive psychophysical procedures. Experiment 2 directly compared performance on the task with that of another quantification method. The results suggested that this objective approach to the study of auditory saltation overcomes difficulties associated with more subjective methods, and provides a reliable paradigm within which to quantify the temporal parameters of saltation on an individual basis.

Acoustic Stimulation↗
PubMed2005

Psychophysical estimates of nonlinear cochlear processing in younger and older listeners.

The primary goal of this project was to compare the performance of younger and older listeners on a number of psychophysical measures thought to be influenced by nonlinear cochlear processing. Younger (mean of 25.6 years) and older (mean of 63.8 years) listeners with normal hearing were matched (within 5 dB) according to their quiet thresholds at the two test frequencies of 1200 and 2400 Hz. They were similarly matched at the adjacent octave frequencies of 600 and 4800 Hz (within 5 dB at one and 9 dB at the other). Performance was compared on measures of auditory filter shape, psychophysical suppression, and growth of forward masking. There was no difference between the two age groups on these psychophysical estimates reflecting nonlinear processing, suggesting that aging per se does not affect the cochlear nonlinearity, at least for the ages sampled here. The results did, however, consistently demonstrate an age-related increase in the susceptibility to forward masking.

Acoustic Stimulation↗
PubMed1990

Physiological mechanisms of psychophysical masking: observations from auditory-nerve fibers.

Masking might be due either to the spread of the excitation produced by the masker to the place of the tone signal along the cochlea or to the suppression of the response to the signal by the masker. In order to identify the contributions of these two mechanisms to tone-on-tone masking, masked thresholds of auditory-nerve fibers were measured in anesthetized cats using the same stimulus paradigms and detection criteria as in psychophysics. Suppressive masking was identified by comparing thresholds for simultaneous masking with those for a nonsimultaneous masking technique resembling pulsation thresholds. These nonsimultaneous thresholds do not include the contribution of suppression to masking because suppression only occurs for stimuli that overlap in time. For each masker and signal frequency, the fibers with the lowest (or "best") masked thresholds had characteristic frequencies (CF) slightly on the opposite side of the masker frequency with respect to the signal frequency, consistent with the psychophysical phenomenon of off-frequency listening. Patterns of best masked thresholds against signal frequency resembled psychophysical masking patterns in that they showed a maximum for signal frequencies close to the masker, and a skew toward high frequencies. Masking was found to be both excitatory and suppressive, with the relative contribution of the two mechanisms depending on the frequency separation between signal and masker. Suppressive masking was large for signal frequencies well above the masker. For these conditions, simultaneous thresholds grew more rapidly with masker level than did nonsimultaneous thresholds, suggesting that the upward spread of masking is largely due to the growth of suppression rather than to that of excitation.

Acoustic Stimulation↗
PubMed1983

Rod and cone activity in patients with dominantly inherited retinitis pigmentosa: comparisons between psychophysical and electroretinographic measurements.

Extended electroretinographic (ERG) testing has been carried out in a series of patients with retinitis pigmentosa, dominantly inherited. In 36 of 57 cases only cone b waves were evoked. In 20 of these, psychophysical tests showed only cones mediated vision (Massof class I), while in 16 statis scotopic perimetry demonstrated residual rod function (class II). In the remaining cases, where rod ERGs were seen, the light intensities required to evoke responses were not greatly elevated. A computer model was constructed to relate psychophysical threshold measurements to ERG data. This analysis of the results suggests that in one subgroup of patients the scotopic ERG is smaller than expected from the losses of visual field and that in another the psychophysical elevation of rod visual threshold is greater than expected from ERG measurements.

Adolescent↗