Abnormal stimulus processing in posttraumatic stress disorder.

This study investigated event-related potential (ERP) indices of information processing in sufferers of posttraumatic stress disorder (PTSD). ERPs were obtained from 18 PTSD patients and 20 controls while they performed a target discrimination task requiring the detection of infrequent target tones from a background sequence of frequent and infrequent distractor tones. A delayed N2 and an attenuated P3 that failed to differentiate target from distractor tones indicated that patients had abnormal difficulty distinguishing task stimuli of differing relevance. It is proposed that this difficulty is reflected behaviorally in the slowed reaction time by patients to target stimuli and may underlie the disturbed concentration and memory impairments found in PTSD. It may also be related to dysfunction in central noradrenaline function, which has been shown to be both crucial in selective attention and abnormal in PTSD.

Enlarged frontal P300 to stimulus change in panic disorder.

This study investigated event-related potential (ERP) indices of information processing in sufferers of panic disorder (PD). ERPs were recorded from 14 PD patients and 15 controls during an auditory target detection task. The task required subjects to discriminate infrequent target tones (p = .14; 2000 Hz) from frequent (p = .72; 1000 Hz) and infrequent (p = .14; 500 Hz) distractor tones. A frontal P300 (P3a) identified in the PD group was characteristic of activity that would be expected to novel, task-irrelevant stimuli and is consistent with junctional pathology involving the prefrontal-limbic pathways. This study provides psychophysiological evidence of an abnormality in PD of the brain's processing of physical changes in the stimulus field that occurs even under conditions of low stimulus load. It may assist in helping to understand the breakdown in information processing that occurs in PD under high load conditions such as crowds and supermarkets.

The effect of clozapine on the speed and accuracy of information processing in schizophrenia.

1. The study aimed to investigate the effects of clozapine on the speed and accuracy of information processing in patients with schizophrenia. Data are reported from 13 subjects with schizophrenia, treated with clozapine for 6.8 (+/- 1.8) months. 2. Reaction time and accuracy of target detection on a tone detection task were measured before and during clozapine treatment, and these results were compared with a matched control group. 3. Symptom severity and performance on three timed tests of cognitive function were also measured prior to clozapine treatment in the schizophrenia group, and these measures were repeated during treatment with clozapine. 4. Treatment with clozapine was found to significantly improve reaction time and the accuracy of target detection in patients with schizophrenia. Despite this improvement their performance remained significantly inferior to that of a matched control group. Both positive and negative symptoms improved with clozapine treatment, as did performance on the WAIS-R digit symbol substitution test. 5. Improved performance on the WAIS-R digit symbol substitution test correlated with reduction in negative symptoms, and faster reaction time showed some correlation with reduction in positive symptoms. 6. The results of this pilot study indicate that treatment with clozapine can produce limited improvement in cognitive function in schizophrenia.

Relationships between changes in symptom ratings, neurophysiological test performance and quality of life in schizophrenic patients treated with clozapine.

This study examined the correlations between reduction in symptoms, changes in neuropsychological test performance and improved quality of life in 19 schizophrenic outpatients treated with clozapine. Reduction in both negative symptoms and general psychopathology was associated with a better quality of life. Some improvement in neuropsychological test performance was found, with a variable pattern of association with change in psychopathology. Improved verbal fluency was associated with reduction in negative symptoms, while improved verbal concept formation was associated with reduction in positive symptoms.

Cortical network dynamics during verbal working memory function.

This study is an exploratory investigation of the regional timing of cortical activity associated with verbal working memory function. ERP activity was obtained from a single subject using a 124-channel sensor array during a task requiring the monitoring of imageable words for occasional targets. Distributed cortical activity was estimated every 2.5 ms with high spatial resolution using real head, boundary element modelling of non-target activity. High-resolution structural MRI was used for segmentation of tissue boundaries and co-registration to the scalp electrode array. The inverse solution was constrained to the cortical surface. Cortical activity was observed in regions commonly associated with verbal working memory function. This included: the occipital pole (early visual processing); the superior temporal and inferior parietal gyrus bilaterally and the left angular gyrus (visual and phonological word processing); the dorsal lateral occipital gyrus (spatial processing); and aspects of the bilateral superior parietal lobe (imagery and episodic verbal memory). Activity was also observed in lateral and superior prefrontal regions associated with working memory control of sensorimotor processes. The pattern of cortical activity was relatively stable over time, with variations in the extent and amplitude of contributing local source activations. By contrast, the pattern of concomitant scalp topography varied considerably over time, reflecting the linear summation effects of volume conduction that often confound dipolar source modelling.

Traumatic lesions of the metatarsophalangeal joint of the great toe in athletes.

In the 1972, 1973, and 1974 football seasons at the University of Arkansas, 74 players sustained sprains of the ankle, producing a total of 152 missed practices and 6 missed games. Although only 18 injuries of the first metatarsophalangeal joint complex were seen, these later resulted in 92 missed practices and 7 missed games. This injury has been a significant problem for both the university and for most other major institutions, judging from a 70% response to 94 questionnaires sent to trainers of 94 large colleges and universities throughout the United States. It is the researchers opinion that the artificial turf surface, particularly as it ages, the shoes, and shoe fitting are all possible contributors to the incidence of the problem. Nonoperative treatment, whose hallmark is rest, is the treatment of first choice. Taping and splinting with a 0.51-mm spring steel splint with reinforcement, both pre- and postinjury, are beneficial. Injections of steroids or any other attempt to return the still painful athlete to activity are contraindicated. Late surgery, particularly in the event of capsular ruptures, as well as early repair, can be of benefit. The need to re-evaluate the shoes and playing surfaces in the light of this and other injuries is emphasized.

Effects of clozapine for non-treatment-resistant patients with schizophrenia.

Clozapine is generally used for patients meeting criteria for treatment resistance. In this study clozapine was given to 19 patients with schizophrenia who did not meet these criteria and whose symptoms were mild to moderate in severity. Clozapine was associated with significant improvement in positive and negative symptoms and quality of life. A more modest improvement on a range of tests of cognitive functioning was also noted. These results suggest that consideration should be given to broadening the usual criteria for patients' eligibility for clozapine treatment.

Ten central elements of family practice.

Previous studies of the content of family practice have analyzed the discipline in terms of the clinical problem content. Taking a different approach, a study group analyzed the care given to patients by family physicians irrespective of the specific clinical problems. Working with a reference group of family physicians in private practice, ten central elements were identified: (1) comprehensiveness of care, (2) anticipation of problems and continuity of care, (3) personal relationships with a patient, (4) medical knowledge and skills characteristic of family medicine, (5) values and attitudes that enhance family medicine, (6) problem definition and medical decision making, (7) problem management and resource coordination, (8) care of the individual within the family context, (9) involvement with the community, and (10) attentiveness to practice organization. This study provides a different point of departure for the design and evaluation of educational programs in family practice.

Suppression and critical bands in band-limiting experiments.

Band-limiting experiments were performed at three noise spectrum levels (N0 = 25, 40, and 55 dB SPL) for forward, simultaneous, and backward masking. Threshold for a 2-kHz sinusoid decreased for masker bandwidths greater than a "critical bandwidth" in nonsimultaneous masking. These results are evidence for a suppression effect not observed in simultaneous masking; however, a qualitative model of suppression can account for the results in all three types of masking. In addition, the data for simultaneous masking support Fletcher's [Rev. Mod. Phys. 12, 47--61 (1940)] rectangular filter interpretation of the band-limiting experiment and are well described by a level-dependent critical band.

Procedure-independent growth-of-masking functions.

The forward-masked threshold for a 10-ms, 1-kHz sinusoidal signal was measured as a function of the level of a narrow-band (60-Hz wide) noise masker at five masker frequencies (0.6, 0.8, 1.0, 1.15, and 1.25 kHz) using both a fixed-masker procedure (determine the threshold level of the signal for a fixed level of the masker) and the converse procedure (determine the masker level necessary to just mask a given signal). A common growth-of-masking function describes the results of both procedures for a given masker frequency; i.e., an identical masker and signal lead to identical performance regardless of which is the dependent variable. The growth-of-masking functions for different masker frequencies show varying degrees of nonlinearity. The nonlinearity of the growth-of-masking functions underlies the discrepancies which arise between masking-pattern and tuning-curve data. These discrepancies do not arise because performance somehow depends upon whether the masker or signal is the dependent variable.

Do off-frequency simultaneous maskers suppress the signal?

Psychophysical tuning curves obtained in forward masking show greater tuning than those obtained in simultaneous masking. This difference is often attributed to the contribution of suppression to the masking produced by off-frequency simultaneous maskers. In this experiment, simultaneous-masking tuning curves were obtained using a 195-ms, 1-kHz sinusoidal signal presented at 40 dB SPL. If the maskers identified in this procedure reduce signal detectability by suppressing the response to the signal, then it should be possible to demonstrate suppression effects between stimuli with the parameters of the masker and signal. One conventional method for demonstrating suppression is to show a reduction in the amount of forward masking produced by one stimulus when a second stimulus is added to it. When used to test the effect of the masker upon the signal, this procedure does not show the suppression supposedly produced by the off-frequency maskers. These data are consistent with an alternative explanation involving only excitatory interactions between masker and signal.

Detection and recognition of auditory patterns.

The detection/recognition theorem (Starr, Metz, Lusted, & Goodenough, 1975) provides a signal detection theory prediction of an observer's ability to identify one of a set of possible signals on the basis of the observer's ability to detect whether any signal is presented. The present findings show that the theorem can be applied to complex auditory stimuli in a fashion that is not merely a trivial extension of the results obtained with simple auditory stimuli.

Combined effect of two suppressors.

Threshold for a 10-ms sinusoidal signal was measured as a function of signal frequency (0.65 to 1.40 kHz) in several forward-masking conditions. For signal frequencies near 1.0 kHz, the forward masking produced by a 395-ms, 100-Hz-wide noise centered at 1.0 kHz (total power 60 dB) could be reduced by the addition of a sinusoid to the noise. The effects of four sinusoidal suppressors (frequencies of 0.70, 0.85, 1.15, and 1.40 kHz, all at 75 dB SPL) were examined individually and in the six possible pairwise combinations. In general, the threshold reduction produced by two suppressors together was no greater than the larger of the reductions produced by the suppressors individually. It appears that suppression produced by different stimuli does not combine to yield significantly larger effects. Instead, the amount of suppression appears to be restricted to a specific range and it is not possible to exceed this limit.

Temporal factors and suppression effects in backward and forward masking.

We discuss several experiments examining the influence of temporal parameters on suppression effects in backward and forward masking. The signal is always a brief 10-ms 2-kHz sinusoid; the masker a narrow band of noise of 40-dB spectrum level, 200-Hz wide, centered at the signal frequency. In some conditions, the presence of a second band of noise of the same spectral level in the region of 2300--3700 Hz appears to suppress the effects of the masker. Changes in the amount of suppression are examined as functions of the delay and duration of the suppressor (experiments 1 and 2). Adding the suppressor during the 50-ms interval nearest the signal produces changes in the signal threshold that are similar to those produced by reducing the level of the masker during this interval for both backward and forward masking (experiment 4). The similarity of these results suggests the operation of peripheral processes common to both backward and forward masking. However, if one increases the duration of the suppressor beyond this 50-ms interval there is no effect on forward masking, but large additional reductions in backward masking. This difference, in conjunction with other recent experiments, suggests the operation of additional central processes in backward masking. For some observers, these additional processes appear to operate over fairly long periods of time (250-500 ms). Such long durations are inconsistent with the estimates of integration time (less than or equal to 200 ms) obtained for these same observers (experiment 3).

Detection and recognition of repeated tones and tonal patterns.

This study examined the effect of multiple presentations on signal detection and on signal recognition (identifying one signal from a set of four possible signals) for three different sets of signals. One set was four sinusoids (100-ms duration, frequencies of 707, 1000, 1414, and 2000 Hz). Two sets contained tonal patterns each made of a sequence of seven, 100-ms, sinusoidal components. In the first set, the four patterns consisted of the same seven sinusoids in different orders. In the second set, the four patterns had the same order of relative frequencies, but had frequencies from different 1/4 oct bands centered at 707, 1000, 1414, and 2000 Hz. All stimuli were adjusted to be equally detectable in the presence of a continuous white noise (eta 0 = 20 dB SPL). Each trial contained 1, 2, 4, 8, or 16 presentations of a given signal plus noise (probability of a signal was 0.5) or noise alone. Detectability of the sinusoids generally increased as the square root of the number of presentations; detectability for the tonal patterns increased at a slower rate. Recognition was generally poorer than predicted by the recognition theorem [S.J. Starr, C. E. Metz, L.B. Lusted, and D.J. Goodenough, Radiology 116, 533-538 (1975)] and increased with multiple presentations only as much as expected from the increase in signal detectability.

Detection of temporally uncertain signals.

The effects of signal uncertainty on detection performance were measured using a new procedure that allows precise specification of the initial temporal uncertainty. Five different models of the detection process, two assuming a continous representation of the sensory input and three assuming a discrete representation, were compared with the obtained data. The effects of varying signal uncertainty (the number of potential signal intervals was one, five, or ten) had little effect on detection performance. The one-parameter form of the choice model can be rejected without hesitation. The continuous Gaussian model and the symmetric two-state model are significantly different from the data. The high threshold and sophisticated two-state models provide accurate descriptions of the data that cannot be rejected on statistical grounds.

Sinusoidal and noise maskers in simultaneous and forward masking.

We compare psychophysical tuning curves obtained with sinusoidal and narrow-band (50-Hz wide) noise maskers in both simultaneous and forward masking. In one experiment, we examine the effects of different combinations of duration and intensity of the 1-kHz sinusoidal signal. In a second experiment, we compare tuning curves obtained with a sinusoidal signal to those obtained with a noise signal. In both experiments, a narrow-band noise is a more effective simultaneous masker than a sinusoid for masker frequencies near the signal frequency. We argue that this is probably due to the use of different detection cues in the presence of sinusoidal and noise maskers, and that the greater masking produced by the noise is not simply due to its greater variability. As observed in other studies, tuning curves are narrower in forward masking than in simultaneous masking.

Suppression effects in backward and forward masking.

The differences in the suppression effect observed in forward and backward masking are consistent with an interpretation that suppression in forward masking results from a reduction of the effective level of the masker in the aditory periphery, and that the suppression in backward masking is influenced by these peripheral processes, but is dominated by additional, central processes. This conclusion is supported by experiments that show differences in the effect of ipsilateral versus contralateral presentation of the suppressor, and differences in the amount of the suppression observed as a function of the level, duration, and frequency of the suppressor.

Forward masking by sinusoidal and noise maskers.

A 2-kHz sinusoid and a narrow-band noise centered at 2 kHz, with the same total power, served as maskers for a 2-kHz sinusoidal signal. We compare the forward masking produced by these two maskers (1) as a function of offset--offset time for 5- and 35-ms signals, (2) as a function of signal duration for a fixed offset--onset time, and (3) as a function of signal duration for a fixed offset--offset time. In all these comparisons, we find that the noise and sinusoid not only produce different amounts of masking for the same experimental condition, but they also show different trends for the same manipulation. The important relations in these results are demonstrated in an additional set of conditions with a 1-kHz signal. In order to account for the differences observed in both experiments, we argue that forward masking is determined by at least two factors. We suggest signal energy as one factor and the presence or absence of differences in quality between masker and signal as another.