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PubMed1993

Absolute sensitivity measured psychophysically and using auditory steady-state potentials.

Absolute thresholds were measured psychophysically (behaviorally) and physiologically in the same subjects. Psychophysical thresholds were obtained using a modified method of limits. Physiological thresholds were based on auditory steady-state potentials recorded from the scalp. The stimuli for both types of test were click trains, periodic tone bursts and amplitude-modulated tones. The center frequency of the bursts and amplitude-modulated tones was 480 or 2000 Hz. It was found that psychophysical thresholds improved, and physiological thresholds worsened as the stimulus became more frequency-specific. Because of this interaction, the differences between psychophysical and physiological thresholds increased monotonically as a function of frequency specificity. Physiological thresholds obtained with the low-frequency stimuli were lower than those acquired with the high-frequency stimuli, while psychophysical thresholds obtained with the two frequencies were essentially the same.

Acoustic Stimulation↗
PubMed2002

Elevated fusiform cell activity in the dorsal cochlear nucleus of chinchillas with psychophysical evidence of tinnitus.

Chinchillas with psychophysical evidence of chronic tinnitus were shown to have significantly elevated spontaneous activity and stimulus-evoked responses in putative fusiform cells of the dorsal cochlear nuclei (DCN). Chinchillas were psychophysically trained and tested before and after exposure to a traumatic unilateral 80 dB (sound pressure level) 4 kHz tone. Before exposure, two groups were matched in terms of auditory discrimination performance (noise, and 1, 4, 6, and 10 kHz tones). After exposure, a single psychophysical difference emerged between groups. The exposed group displayed enhanced discrimination of 1 kHz tones (p = 0.00027). Postexposure discrimination of other stimuli was unaffected. It was hypothesized that exposed animals experienced a chronic subjective tone (i.e., tinnitus), resulting from their trauma, and that features of this subjective tone were similar enough to 1 kHz to affect discrimination of 1 kHz objective signals. After psychophysical testing, single-unit recordings were obtained from each animal's DCN fusiform cell layer. Putative fusiform cells of exposed animals showed significantly (p = 0.0136) elevated spontaneous activity, compared with cells of unexposed animals. Putative fusiform cells of exposed animals showed a greater stimulus-evoked response to tones at 1 kHz (p = 0.0000006) and at characteristic-frequency (p = 0.0000009). This increased activity was more pronounced on the exposed side. No increase in stimulus-evoked responses was observed to other frequencies or noise. These parallel psychophysical and electrophysiological results are consistent with the hypothesis that chronic tonal tinnitus is associated with, and may result from, trauma-induced elevation of activity of DCN fusiform cells.

Acoustic Stimulation↗
PubMed2003

Response suppression in v1 agrees with psychophysics of surround masking.

When a target stimulus is embedded in a high contrast surround, the target appears reduced in contrast and is harder to detect, and neural responses in visual cortex are suppressed. We used functional magnetic resonance imaging (fMRI) and psychophysics to quantitatively compare these physiological and perceptual effects. Observers performed a contrast discrimination task on a contrast-reversing sinusoidal target grating. The target was either presented in isolation or embedded in a high-contrast surround. While observers performed the task, we also measured fMRI responses as a function of target contrast, both with and without a surround. We found that the surround substantially increased the psychophysical thresholds while reducing fMRI responses. The two data sets were compared, on the basis of the assumption that a fixed response difference is required for correct discrimination, and we found that the psychophysics accounted for 96.5% of the variance in the measured V1 responses. The suppression in visual areas V2 and V3 was stronger, too strong to agree with psychophysics. The good quantitative agreement between psychophysical thresholds and V1 responses suggests V1 as a plausible candidate for mediating surround masking.

Contrast Sensitivity↗
PubMed1990

Electrophysiological and psychophysical flicker sensitivity in patients with primary open-angle glaucoma and ocular hypertension.

Temporal sensitivity was assessed in patients with primary open-angle glaucoma (POAG) and ocular hypertension (OHT). Three measures of flicker sensitivity were obtained: psychophysical modulation thresholds, visual-evoked potentials (VEPs), and focal electroretinograms (FERGs). We found elevated psychophysical thresholds at higher temporal frequencies (30-50 Hz) in patients with POAG, relative to thresholds for age-matched controls. The OHT patients had elevated psychophysical thresholds only at 50 Hz. On the other hand, VEP amplitudes in POAG patients were reduced at all temporal frequencies, with the magnitude of the loss increasing with temporal frequency. The OHT patients, however, showed no reductions in VEP amplitude at any temporal frequency. Finally, POAG patients' FERG amplitudes were reduced at 30-50 Hz; whereas FERG amplitudes in the OHT patients were normal at all temporal frequencies. These results indicate that OHT patients can exhibit psychophysical threshold losses at high temporal frequencies which are not observed in the suprathreshold electrophysiological amplitude measures. On the other hand, patients with POAG show both psychophysical and VEP losses across a range of temporal frequencies. In addition, the decreases in FERG amplitudes in POAG patients suggest changes in the functioning of the outer retina in this disease.

Adult↗
PubMed1990

Tactile roughness: neural codes that account for psychophysical magnitude estimates.

Hypothetical neural codes underlying the sensation of tactile roughness were investigated in a combined psychophysical and neurophysiological study. The stimulus set consisted of plastic surfaces embossed with dot arrays of varying dot diameter and center-to-center spacing. Human subjects explored each surface with the pad of the index finger and reported their subjective sense of roughness magnitude. The same surfaces were scanned across the receptive fields of cutaneous mechanoreceptive afferents in monkeys while recording the evoked action potentials. Hypothetical neural codes for roughness magnitude were computed from the neural response patterns and tested for their ability to account for the psychophysical data. The psychophysical results showed that subjective roughness magnitude is an inverted U-shaped function of dot spacing that peaks near 3.0 mm spacing, and that increased dot diameter produces decreased roughness sensations at all dot spacings. Hypothetical neural codes that do not bear a consistent relationship to roughness magnitude across all of these stimulus conditions can be rejected as the code for roughness. Four types of neural codes were considered. They were based on (1) mean firing rate, (2) general variation in firing rate, (3) short-term temporal variation in firing rate, and (4) local spatial variation in firing rate. Mean firing rate failed to explain the psychophysical results: surfaces that evoked the same firing rate often evoked very different roughness judgments. In contrast, neural codes based on firing-rate variation, especially in slowly adapting afferents, account for the psychophysical results.

Action Potentials↗
PubMedDate not supplied

Psychophysical testing in human populations exposed to neurotoxicants.

Sensory organs can be studied from different points of view: biochemical, morphological, electrophysiological, clinical, and psychophysical. In this paper, the psychophysical and electrophysiological approaches are discussed and compared. Even though close parallels have been drawn between these two methodologies, discrepancies clearly indicate that they do not measure the same phenomenon. Vibration sensitivity is used to illustrate the role sensory assessment plays in neurotoxicology. Several psychophysical techniques are described to measure this sensory modality. Emphasis is placed on the need to quantitatively define stimulus parameters. The validity of vibration sensitivity as an indicator of sensory peripheral nerve dysfunction is established through a review of diseases, physical agents, pharmaceuticals, and other neurotoxicants known to alter the morphology and/or the physiology of the peripheral nervous system or sense organs. A series of factors or conditions affecting vibration detection thresholds, such as age, laterality, gender, temperature and others, are examined. Finally, a review of the psychophysical methods and procedures illustrates the advantages of the forced-choice paradigm and the tracking technique over other procedures and methods of stimulus presentation. The importance of psychophysical assessment of sensory functions in neurotoxicology is emphasized.

Electrodiagnosis↗
PubMed1980

Differences of CT (2f1 - f2) phase in psychophysical and physiological experiments.

Neural and psychophysical studies of combination tones (CT) give highly correlated evidence for the existence of stimulus-like intracochlear distortion products. However, a large systematic difference was found between psychophysical and neural measurements of the phase of the cubic CT, 2f1 - f2. The psychophysical phase, as measured by monaural concellation, decreases typically at 6-12 degrees per decibel increase in stimulus amplitudes, while the physiological phase, measured both by neural phase locking or by cancellation of the locking, is nearly independent of stimulus amplitudes. Through new psychophysical studies of combination tone interactions monaurally as well as their lateralization binaurally, we examined whether the phase of the psychophysical cancellation tone directly measures the phase of the intracochlear CT. We found evidence for amplitude dependent biases in the cancellation measurement, but the biases were generally far too small to account for the amplitude dependence of the cancellation phase. On the other hand, binaural lateralization of the CT showed a similar amplitude dependence of CT phase as found in monaural cancellation. No evidence exists in neural data either for an amplitude dependent bias of the cancellation measurement or for systematic amplitude dependence of the neural phase. Therefore, we conclude that a real difference exists in the intracochlear nonlinearity for alert human subjects and anaesthetized laboratory animals. We model the human cochlea nonlinearities by modifying Hall's nonlinear transmission line model through the addition of nonlinear stiffness in the nonlinear mechanical loading of the basilar membrane.

Animals↗
PubMed2006

Auditory event-related potentials differ in dyslexics even when auditory psychophysical performance is normal.

Developmental dyslexia is characterized by a phonological processing deficit and impaired low-level auditory processing may contribute to this problem. However, this remains controversial because not all dyslexic individuals show psychophysical deficits on auditory processing tasks; hence it has been argued that auditory processing deficits are not a causal factor in dyslexia. Because behavioral psychophysical tasks include both bottom-up processing and top-down strategies, dyslexics' successful coping strategies may positively influence their performance on auditory behavioral measures. Therefore we have studied whether dyslexics who perform adequately on auditory psychophysical tasks nevertheless show electrophysiological evidence of impaired auditory processing. We compared auditory event-related mismatch negativity (MMN) potentials to frequency modulated (FM) tones at 5, 20 and 240 Hz between dyslexic adults and controls. Groups were matched for age, cognitive ability and psychophysical FM detection thresholds. The dyslexic group showed significantly smaller MMNs in the 20 Hz FM condition in both the early (150-300 ms, P=0.010) and late (300-500 ms, P=0.049) time frames. A 2-way ANOVA showed a significant group by FM rate interaction (P=0.012). There were no significant differences between the groups in the 5 Hz or 240 Hz conditions. The magnitude of the 20 Hz FM MMN correlated with the degree of discrepancy between cognitive and literacy skills (0.66, P=0.003) in the entire group. Thus, even among compensated dyslexics with above-average cognitive abilities and adequate performance on auditory psychophysical tasks, the MMN responses of some dyslexic adults were found to be abnormal.

Adult↗
PubMed1997

Comparison of psychophysical and evoked potential methods in the detection of visual deficits in multiple sclerosis.

We compared the diagnostic sensitivity of traditional visual tests such as the Snellen-test and pattern reversal VEPs with psychophysical and electrophysiological tests involving motion processing and psychophysical tests of contrast processing in detecting visual deficits in a group of MS patients. A total of 30 patients with a definite diagnosis of MS and 22 age-matched controls selected from a pool of healthy volunteers participated in this study. Visual evoked potentials elicited by reversing checkerboards and moving random dot patterns (motion-onset VEPs) were recorded. The recognition of motion-defined forms (motion-defined letter test, MDL-test) and of contrast reduced optotypes was measured psychophysically. Of 30 patients, 29 showed deficits in at least one of the tests applied. The highest detection rate was obtained for a simple psychophysical test, the MDL-test, which revealed abnormalities in 80% of the patients. This is about 12% more than pattern VEPs could detect. Conversely, abnormalities in motion-onset VEPs were found in only 16% of the patients. Our results show that by adding a simple psychophysical test of form-from-motion analysis our capability to demonstrate an involvement of the visual system in MS patients may be promoted considerably.

Adult↗
PubMed1995

Psychophysical tuning curves in subjects with tinnitus suggest outer hair cell lesions.

A study by Penner (J Speech Hear Res 1980;23:779-86) found evidence for impaired lateral suppression in subjects with tinnitus and sensorineural hearing loss. If lateral suppression is related to tuning curve sharpness and lateral suppression is impaired, the shape of the tuning curve should be affected. The purpose of this study was to determine whether subjects with tinnitus have psychophysical tuning curves that are different from those of subjects without tinnitus. Psychophysical tuning curves and hearing thresholds were obtained from 18 subjects, 7 with tinnitus and 11 without tinnitus. Only subjects with normal audiograms (through 8 kHz) were selected for this study. In subjects with tinnitus psychophysical tuning curves were obtained in the region pitch-matched to their tinnitus. In nontinnitus subjects psychophysical tuning curves were determined at the same frequencies as for the tinnitus subjects in a yoked-control design. The slopes of the tails and tips and the Q10 and other measures were calculated for each tuning curve. The psychophysical tuning curves in subjects with tinnitus were significantly different (0.01 level) from those of control subjects and often had hypersensitive tails and some elevated tips. These shapes of tuning curves are consistent with cochlear lesions involving the loss of outer hair cells without damage to the inner hair cells or nerve fibers.

Adolescent↗
PubMed1990

Psychophysical measures of central auditory dysfunction in multiple sclerosis: neurophysiological and neuroanatomical correlates.

Central auditory function was assessed in 15 patients with multiple sclerosis (MS) to determine whether the demyelinating lesions resulted in disruption of temporal processing. Auditory evoked potential (AEP) recordings included all three latency regions: Auditory brain stem responses (ABRs), midlatency responses (MLRs), and long-latency responses (LLRs). Two psychophysical tasks thought to involve temporal processing were used: a monaural-processing task (gap-detection) and a binaural-processing task (masking level difference; MLD). Further, AEP abnormalities and psychophysical performance deficits were related to lesion location, based on magnetic resonance imaging (MRI) scans. Reduced MLDs were seen in six MS subjects. Abnormal MLDs were always accompanied by abnormal ABRs and MLRs, and compared to subjects with normal MLDs, the subjects with abnormal MLDs were more likely to have bilateral abnormalities in the AEPs. Further, MLR indices of abnormal binaural interaction appeared to be specifically related to the psychophysical measure of binaural processing. The MRI data of these patients indicated widespread involvement of the auditory pathway. MS subjects with abnormal MRI signals restricted to levels caudal to the lateral lemniscus did not have abnormal MLDs. Gap-detection thresholds were more resistant to the effects of the demyelinating lesions; only two subjects had abnormal gap-detection thresholds. These subjects had extensive AEP abnormalities (bilaterally, in all three latency regions). The gap-detection thresholds were most specifically related to abnormalities of the LLRs. In addition, the subjects with elevated gap-detection thresholds were the only ones with a prolonged interval between the ABRs and MLRs. Thus, efficient neural conduction between the upper brain stem and auditory cortex appears to be crucial for normal monaural temporal processing. The results indicate that demyelinating lesions can cause deficits in temporal processing in the central auditory pathway. However, auditory temporal processing is not a unitary phenomenon since abnormalities at different levels of the auditory system disrupt different types of temporal processing. Finally, abnormal psychophysical performance was not seen in all subjects with AEP and MRI evidence of involvement of the auditory pathway; rather, these psychophysical measures appeared to be sensitive to disruption only in specific portions of the auditory system.

Adolescent↗
PubMed1996

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 as d' 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 by d'-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.

Adult↗
PubMed1992

[Psychophysical load of students in the first year of community secondary schools].

The material comprised 179 first-grade pupils (92 girls and 87 boys) of private high-schools in several big cities. The psychophysical load of pupils was evaluated using a standard questionnaire containing 77 questions. These questions were arranged in groups allowing for estimation of psychophysical load related to school lessons, extracurricular activities, daily timetable, pupil's situation in the class and family, and his psychic feeling. The results were treated statistically; moreover, they were compared with the results of earlier studies on 518 first-grade pupils (346 girls and 172 boys) of public high-schools in the same cities. The results lead to the following conclusions: In both private and public high-schools the psychophysical load of girls exceeded that of boys. Likewise, the objectively existing load-causing situations and subjective feelings of the troublesomeness of these situations were a greater nuisance to girls. Psychophysical loads of these girls and boys were somewhat slighter in private than in public high-schools. This decrease in psychophysical load of girls and boys attending private high-schools is associated with smaller loads related to school lessons and to the pupil's situation in the family and class, as well as is due to his better psychic feeling. Loads related to extracurricular activities were similar for girls and boys, irrespective of the kind of high-school. Loads associated with school timetable were in private schools similar for girls and boys, whereas in public schools they were somewhat higher for girls.

Adolescent↗
PubMed1989

[Changes in psychophysical loads of junior high school students as a result of the educational reform].

Prior to introduction of changes in the education programme in 1985/1986 a group of 400 students (277 girls and 123 boys) were examined. They were in the first class of the colleges in several cities. One year later, after a reform of the education programme, another group of first-year students were tested (212 girls and 117 boys) in the same schools. The psychophysical strain of the students was assessed by means of a standardized inquiry containing 77 questions grouped so that it was possible to assess the psychophysical strain connected with school education, work outside school, timing of work during a day, situation in the class and in the family, and psychic wellbeing. The sum of the points obtained in the answers provided information about the general psychophysical strain. The answers to certain questions described objectively the stressful situations and the subjective experiencing of the difficulties of them. Psychophysical strain of first class students before and after the introduction of changes in the education programme differed between girls and boys. The strain experienced by girls was greater than that of boys, but the changes in the education programme decreased the difference between them in the intensity of strain. The reform of the education programme increased the total psychophysical strain of girls and boys, due to increased strain related to the objective stressful situations of first class students and to subjective experiencing of this strain.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

[Comparison of psychophysical stress in students in the first and second grades at secondary schools].

The study was carried out on 298 students (216 girls and 82 boys) beginning education in the first classes of secondary schools in Bydgoszcz, Cracow and Poznań. After one year the same students were examined again (282 second class students, 197 girls and 85 boys). The psychophysical stress was determined using an inquiry with 77 questions grouped in such a way that it was possible to pinpoint stress related to school education, work outside school, day timetable, situation of the student in class and family, and psychic wellbeing. The total score of all answers provided information on the total psychophysical stress. The answers to the questions pointed to the stressful factors and subjective feeling of the troublesomeness of these factors. It was found that with longer time spent in school the psychophysical stress was increasing. Although the stress resulting with objectively existing situations was at a similar level in both compared classes in the case of girls, and was slightly higher in the second class for boys, the subjective feeling of troublesomeness of these situations increased evidently in the second year both for boys and girls. The psychophysical stress of students in both compared classes differed for both sexes. In girls the psychophysical stress, subjective feeling of troublesomeness of work related to lessons, work timetable, student's situation in class and family and psychic wellbeing were greater in the first and second year of education. Only the magnitude of stress connected with work outside school was similar for boys and girls, and it was similar in both compared classes. The obtained results suggest the need for a differential approach during education to girls and boys, since girls are more susceptible to the effects of various stressful factors.

Activities of Daily Living↗
PubMed1999

Psychophysical study of noxious and innocuous cold discrimination in monkey.

Psychophysical evidence shows that humans are better able to distinguish differences in the intensity of cutaneous temperature in the cool range than in the noxious cold range. In order to compare these human perceptual findings with physiological data from non-human primates, we performed similar psychophysical experiments of cold perception in monkeys. Two adult male rhesus monkeys were trained to detect cooling shifts from baseline temperatures between 0 degrees and 22 degrees C applied to the face with a 1-cm2 contact thermode. Detection thresholds were determined using the method of constant stimuli for one monkey and an adaptive psychophysical algorithm which insured constant behavioral performance for the other monkey. Results showed that both monkeys detected significantly smaller temperature decreases from innocuous cool baselines (i.e., 22 degrees and 16 degrees C) than from noxious and near-noxious baselines (10 degrees, 6 degrees, 0 degrees C). Similarly, the latencies for detecting the cooling shifts were shorter and less variable in the innocuous cool range than in the noxious cold range. The observation of more precise discrimination of innocuous cool than noxious cold temperatures in monkeys is consistent with human psychophysical data. Thus, these data suggest that differential patterns of neuronal activity evoked by cool and noxious cold cutaneous stimuli, observed in peripheral afferents as well as in the central nervous system of monkey and cat, probably also exist in the human.

Adaptation, Physiological↗
PubMed1994

Low luminance contrast sensitivity: effects of training on psychophysical and optokinetic nystagmus thresholds in man.

We compared psychophysical contrast sensitivity function (psi-CSF) and optokinetic contrast sensitivity function (OKN-CSF) in man, for the combination of three spatial and three temporal frequencies. psi-CSF was defined as the inverse of the contrast threshold, that is the contrast value of a sinusoidal grating for which a subject was able to identify the width of a drifting grating. OKN-CSF was defined as the inverse of the contrast value of the grating which triggered an involuntary optokinetic nystagmus. In highly experienced subjects, OKN-CSF was overall higher than psi-CSF. More precisely, differences between both contrast sensitivity functions occurred mainly in the low spatio-temporal frequency range (below 4 c/deg and 9 Hz). In naive subjects, psi-CSF reached the level of OKN-CSF after two consecutive test sessions. OKN-CSF did not change with training. Similarly, high spatio-temporal frequency psychophysical thresholds did not change with training and, moreover, approximated OKN-CSF thresholds. Low spatio-temporal frequency psychophysical sensitivity was initially lower than corresponding OKN-CSF sensitivity; however, after only two training sessions, the two functions were indistinguishable due to a selective increase in psychophysical low spatio-temporal frequency sensitivity.

Adult↗
PubMed1995

Functional responses from guinea pigs with cochlear implants. I. Electrophysiological and psychophysical measures.

We examined electrophysiological and psychophysical measures of the electrically stimulated auditory system of guinea pigs implanted with chronic intracochlear electrodes. Guinea pigs were trained to detect low-level acoustic stimuli and then unilaterally deafened and implanted with one extracochlear and two intracochlear electrodes. Electrically evoked auditory brainstem responses (EABRs) and psychophysical detection thresholds were obtained from the same animals using pulsatile stimuli. Supplementary EABR data were obtained from additional, untrained, animals. Thresholds were obtained as a function of stimulus phase duration and monopolar and longitudinal-bipolar electrode configurations. The slopes of the EABR and psychophysical functions for bipolar stimulation, averaged across subjects within 1 month after implantation, were -5.25 and -6.18 dB per doubling of pulse duration, respectively. These slopes were obtained with pulse durations ranging from 20 to 400 microseconds/phase; slope was reduced at longer pulse durations. Strength-duration slope also varied as a function of electrode configuration: monopolar stimulation produced steeper functions than did bipolar stimulation. Differences between EABR and psychophysical strength-duration measures suggest the existence of central mechanisms of stimulus integration in addition to that occurring at the level of the auditory nerve. Differences observed with variation of stimulus parameters (e.g., monopolar vs. bipolar stimulation modes) suggest that the specific mode of intracochlear electrical stimulation can influence stimulus integration. Such observations may be useful in the design of prosthetic devices and furthering our understanding of electrical excitation of the auditory system.

Acoustic Stimulation↗