Biomedical subjects

P T Michie

Publications and source records attributed to P T Michie.

At least 19 recordsLinked to original sources

PubMed2000

ERP correlates of response inhibition to elemental and configural stimuli in a negative patterning task.

OBJECTIVE: The present experiment examined the ERP correlates of response inhibition to elemental and configural Nogo stimuli in a Go/Nogo task. DESIGN AND METHODS: Event-related potentials (ERPs) were recorded while 8 subjects completed a visual Go/Nogo task. Nogo stimuli required the inhibition of a response to stimuli that differed from Go stimuli (A+, B+) either on the basis of each of two physical features (elemental Nogo stimuli; CD-) or on the basis of the conjunction of features represented in the Go stimuli (configural Nogo stimuli; AB-). Behavioural data and ERP component measures (amplitude and latency) were analysed using analysis of variance. RESULTS: An enhanced N2 component and an enhanced fronto-centrally distributed P3 component were elicited following elemental Nogo stimuli relative to Go stimuli, consistent with a number of studies examining ERPs during Go/Nogo tasks. In contrast, an enhanced late frontal negative/parietal positive slow wave was elicited following configural Nogo stimuli relative to Go stimuli. CONCLUSIONS: These results cast doubt on the interpretation of the N2 enhancement as reflecting response inhibition processes per se. The pattern of results was interpreted as providing support for the unique cue model of learning rather than the configural model of learning and was discussed in the context of a recent model of executive functioning.

Adult↗

PubMed2000

Duration and frequency mismatch negativity in schizophrenia.

OBJECTIVES: The aim of the present study was to elucidate the reasons for apparent inconsistencies in the schizophrenia literature with respect to the mismatch negativity (MMN) waveform of the event-related potential (ERP). While most previous research has shown that MMN is reduced in schizophrenia, there are a small number of studies reporting that frequency MMN is not reduced. METHODS: We recorded ERPs to auditory stimuli with different frequencies and durations from patients with schizophrenia (N = 14) and control subjects (N = 17) of similar age and sex. MMNs to small but discriminable frequency deviants were contrasted with large frequency deviants and duration deviants. RESULTS: Only the MMN to duration deviants was significantly reduced in patients, although there was evidence of a similar trend for large frequency deviants. CONCLUSIONS: The results together with a review of the frequency MMN literature suggest that there are 3 variables which are important in determining whether patients exhibit a reduced MMN to frequency deviants: deviant probability, degree of deviance and interstimulus interval. The results also indicated that patients with schizophrenia may have particular deficits in processing the temporal properties of auditory stimuli. This finding has implications for the pathophysiology of the disorder as time-dependent processing is reliant on the integrity of an extensive network of brain areas consisting of auditory cortex, areas of pre-frontal cortex, the basal ganglia and cerebellum.

Acoustic Stimulation↗

PubMed2000

The effects of cigarette consumption on the Sternberg visual memory search paradigm.

AIM: To examine the performance of non-smokers (n = 24), light smokers (n = 22, mean 6.5 cigarettes per day) and heavy smokers (n = 19, mean 23 cigarettes per day) on the Sternberg memory search task. DESIGN: A repeated-measures, counterbalanced design was used with one between-subject factor, status (heavy, light or non-smoker) and two within-subject factors, condition (12 hours abstinence or ad libitum smoking) x time (pre- or post-cigarette). FINDINGS: Heavy smokers in the pre-cigarette abstinent session had significantly slower reaction times, movement times and higher intercepts (a measure of factors contributing to performance other than rate of memory scan) than non-smokers. After smoking these differences were removed. CONCLUSIONS: This suggests that rather than improving performance smoking ameliorates a deficit in certain measures of the Sternberg task produced by abstinence. Under ad libitum conditions improvements in performance were attributed to practice. Across all within-subject conditions, there were no significant main effects of smoking status, and this result was consistent with the lack of relationship between measures of saliva continine and expired air carbon monoxide and performance. These data do not support the view that non-abstinent smokers differ from non-smokers in the performance of the Sternberg memory search procedure.

Adolescent↗

PubMed2000

Dissociable cognitive impairments in problem drinkers.

Patients in a treatment programme for severe alcohol dependence were tested on a battery of tests designed to examine organizational and visuo-spatial abilities. Analysis using a case-study approach indicated independent organizational and visuo-spatial impairments. An understanding of aetiological factors underlying these cognitive deficits and implications for treatment are discussed.

Adult↗

PubMed1999

An exploration of varieties of visual attention: ERP findings.

A set of five tasks was designed to examine dynamic aspects of visual attention: selective attention to color, selective attention to pattern, dividing and switching attention between color and pattern, and selective attention to pattern with changing target. These varieties of visual attention were examined using the same set of stimuli under different instruction sets; thus differences between tasks cannot be attributed to differences in the perceptual features of the stimuli. ERP data are presented for each of these tasks. A within-task analysis of different stimulus types varying in similarity to the attended target feature revealed that an early frontal selection positivity (FSP) was evident in selective attention tasks, regardless of whether color was the attended feature. The scalp distribution of a later posterior selection negativity (SN) was affected by whether the attended feature was color or pattern. The SN was largely unaffected by dividing attention across color and pattern. A large widespread positivity was evident in most conditions, consisting of at least three subcomponents which were differentially affected by the attention conditions. These findings are discussed in relation to prior research and the time course of visual attention processes in the brain.

Adolescent↗

PubMed1998

Decrement of the N1 auditory event-related potential with stimulus repetition: habituation vs. refractoriness.

We examined whether the amplitude decrement traditionally found for the N1 peak of the event-related potential (ERP) with repetition of auditory stimuli results from the process of habituation or from the refractory period of the neural elements underlying the N1 response. These competing accounts of the process underlying the N1 decrement with repetition differ in terms of the predicted effects of variations in stimulus repetition and interstimulus interval (ISI). These predictions were examined using a short-term habituation design with a factorial combination of stimulus repetition and ISI. Forty-five subjects received 21 stimulus trains, each consisting of seven innocuous tones, all at 1 kHz except the sixth, which was a 1.5-kHz tone. Each subject was assigned to one of three ISI conditions (either 1, 3 or 10 s). The results provide little support for the view that N1 response decrement with stimulus repetition reflects a process of habituation. The present results provide greater support for the view that this decrement is based on the separate refractory periods or recovery cycle processes of at least two neural generators contributing to activity in the N1 peak latency range.

Acoustic Stimulation↗

PubMed1998

Further evidence for a deficit in switching attention in schizophrenia.

In this study, sustained, selective, divided, and switching attention, and reloading of working memory were investigated in schizophrenia by using a newly developed Visual Attention Battery (VAB). Twenty-four outpatients with schizophrenia and 24 control participants were studied using the VAB. Performance on VAB components was correlated with performance of standard tests. Patients with schizophrenia were significantly impaired on VAB tasks that required switching of attention and reloading of working memory but had normal performance on tasks involving sustained attention or attention to multiple stimulus features. Switching attention and reloading of working memory were highly correlated with Trails (B-A) score for patients. The decline in performance on the switching-attention task in patients with schizophrenia met criteria for a differential deficit in switching attention. Future research should examine the neurophysiological basis of the switching deficit and its sensitivity and specificity to schizophrenia.

Adult↗

PubMed1997

Evidence of visual processing negativity with attention to orientation and color in central space.

The aim of this study was to determine whether the visual frontal processing negativity reported in our earlier paper (Karayanidis, F. and Michie, P.T. Electroenceph. clin. Neurophysiol., 1996, 99: 38-56) is related to selection of spatial location, or occurs regardless of the stimulus features used to define the target. Subjects were instructed to respond to infrequent target stimuli of a particular combination of orientation, color and size. All stimuli were presented at central fixation. Posteriorly, orientation selection enhanced P125 amplitude over the right hemisphere but neither orientation nor color selection had an effect on N190. Posterior selection negativities emerged for orientation, color and their conjunction. At anterior sites, widespread effects of orientation and color processing were evident. The effect of location selection on the anterior N1 seen in our previous study was not evident with orientation selection. Instead, selection of orientation, color and their conjunction resulted in P145-250 frontally. Two later anterior negativities emerged. The early negativity (vPNe) was affected independently by orientation and color selection while the late negativity (vPNl) was affected only by selection of feature conjunction. Thus, the present results show that, like its auditory counterpart, the visual processing negativity occurs with a variety of stimulus classification features and is not exclusively related to spatial selection.

Adolescent↗

PubMed1996

Evoked otoacoustic emissions and auditory selective attention.

The auditory system has an extensive peripheral efferent innervation. The question addressed in this paper is whether the olivocochlear bundle (OCB) efferent system innervating the outer hair cells (OHC) of the cochlea plays a role in selective attention. As evoked otoacoustic emissions (EOAE) provide a measure of the active micromechanical properties of OHCs, they can be used to assess the role of the efferent system in attention. Six experiments using tone-pip EOAEs are reported. In each experiment, EOAEs generated by 1 or 2 kHz tone pips when they were attended were compared with EOAEs to the same stimuli when they were unattended. In three experiments (1-4), a non-linear stimulus difference method was used to record a pure cochlear component of EOAEs. In Exps. 1-5, 1 and 2 kHz tone pips were delivered to the same ear and the difficulty of the subjects' task was manipulated in order to produce a more focussed attentional state or contralateral noise was presented to determine whether attention effects are dependent upon having an already activated efferent system. In Exp.6, the 1 and 2 kHz stimuli were delivered to opposite ears. A total of 70 subjects participated in the six experiments. There were no effects of attention on EOAEs in any of the experiments in the direction of previously reported effects. The results of these first six experiments employing simple attention switches between fixed auditory objects do not support active cochlear involvement in selective attention.

Acoustic Stimulation↗

PubMed1996

Frontal processing negativity in a visual selective attention task.

The auditory processing negativity has been associated with the maintenance of an internal representation of context and has been shown to be dependent on the integrity of the prefrontal cortex. Previous visual selective attention studies have failed to show consistent evidence of a frontal processing negativity. The present study employed a multi-dimensional visual selective attention task, modelled after Hillyard and Munte (Percept. Psychophys., 1984, 36: 185-198). Subjects responded to infrequent target stimuli of a particular location, color and height combination, while ignoring all stimuli differing from the target on any of these dimensions. Consistent with previous literature, at posterior sites, location selection resulted in enhancement of P1 and N1 amplitude, followed by color selection within the attended location at around 200 ms. These effects were most pronounced contralaterally. However, unlike previous studies, a large prolonged processing negativity was evident at all frontal sites. This effect involved three components, an early frontally negative component peaking around the N1, a frontocentral negativity maximal at 300 ms and a long-lasting widespread negativity beginning after 500 ms. Processing of location preceded the onset of color and location/color conjunction processing, suggesting hierarchical stimulus feature analysis. However, at posterior temporal sites there was evidence of parallel color processing in the unattended location.

Adolescent↗

PubMed1995

Differential impairments of selective attention due to frequency and duration of cannabis use.

The evidence for long-term cognitive impairments associated with chronic use of cannabis has been inconclusive. We report the results of a brain event-related potential (ERP) study of selective attention in long-term cannabis users in the unintoxicated state. Two ERP measures known to reflect distinct components of attention were found to be affected differentially by duration and frequency of cannabis use. The ability to focus attention and filter out irrelevant information, measured by frontal processing negativity to irrelevant stimuli, was impaired progressively with the number of years of use but was unrelated to frequency of use. The speed of information processing, measured by the latency of parietal P300, was delayed significantly with increasing frequency of use but was unaffected by duration of use. The results suggest that a chronic buildup of cannabinoids produces both short- and long-term cognitive impairments.

Adolescent↗

PubMed1995

ERP indices of auditory selective attention in aging and Parkinson's disease.

In the present study, we compared the performance of normal subjects in three age groups and of medicated Parkinson's disease patients on auditory selective attention processes. Two tone sequences were dichotically presented. Subjects responded to deviant tones in the attended location. Event-related potentials (ERPs) were recorded from nine scalp electrodes. The old group showed significant decline in hit rate, increase in N1 amplitude, and reduction in P3a, P3b, target negativity, and mismatch negativity amplitude. The amplitude and duration of late Nd increased with age, reflecting modulation of both attended and unattended standard ERPs. Although the middle group showed a similar pattern of ERP changes, the effects were generally nonsignificant. The Parkinson's disease group showed little further disruption of behavioral or ERP measures. However, Parkinson's disease affected late Nd in the direction opposite of that of aging, reflecting differential modulation of unattended standard positivity.

Acoustic Stimulation↗

PubMed1995

Brain potential evidence for an auditory sensory memory deficit in schizophrenia.

OBJECTIVE: The multiple disorders of selective attention found in schizophrenia could be secondary to disturbances in sensory processing. The authors investigated this possibility by using an event-related potential index of auditory sensory memory, called "mismatch negativity." METHOD: Medicated (N = 11) and neuroleptic-free (N = 11) patients with schizophrenia and patients with bipolar affective disorder (N = 11) were compared with age- and sex-matched healthy comparison subjects. Auditory stimuli were presented while the subjects were distracted with an attention-demanding visual task. Event-related potentials were elicited by infrequently occurring auditory stimuli (deviants) and by regularly presented auditory stimuli (standards), which differed slightly in duration. The difference in amplitude between the event-related potentials elicited by the deviant and standard stimuli was the mismatch negativity. RESULTS: The amplitude of the mismatch negativity was significantly lower in both groups of schizophrenic patients than in the healthy comparison subjects. Mismatch negativity amplitude was significantly correlated with ratings of negative schizophrenic symptoms but not with positive symptoms. Compared with the matched comparison subjects, the bipolar affective disorder patients did not show lower amplitude of mismatch negativity. There was a significant negative correlation between age and mismatch negativity amplitude. CONCLUSIONS: The abnormal auditory sensory memory processing indicated by low mismatch negativity amplitude in the schizophrenic patients cannot be accounted for by neuroleptic medication status. Because this abnormality was significantly related to measures of negative symptoms only, it may be a chronicity marker or reflect a predisposition to the development to schizophrenia. These findings implicate the auditory cortex in the pathophysiology of schizophrenia.

Acoustic Stimulation↗

PubMed1995

Memory functioning in social drinkers: a study of event-related potentials.

Verbal memory functioning was assessed in light and heavy social drinkers by recording event-related potentials in subjects instructed to memorize lists of words using either repetition or elaborative learning strategies. Although overall performance did not differ significantly between light and heavy drinkers, heavy drinkers showed reduced within-list organization compared with light drinkers. There were statistically significant differences in the event-related potential indices of memory functioning elicited during complex elaborative processing which were consistent with decreased within-list organization in heavy drinkers.

Adult↗

PubMed1994

Facilitation of the N1 peak of the auditory ERP at short stimulus intervals.

Event-related potentials (ERP) were recorded to 1 kHz tones presented at random stimulus onset asynchronies (SOA) between 100 and 1000 ms. The Adjar correction procedure was employed to overcome waveform distortion resulting from previous response overlap. The results showed dramatic enhancements of the N1 peak when SOA was reduced to 100-300 ms, showing a reversal of the traditional amplitude by SOA function obtained by previous ERP research employing SOAs > 500 ms, and replicating similar enhancements of the magnetic counterpart of the N1 (N100m). The results are discussed in terms of the utility of the traditional 'refractoriness' account of the sensitivity of the N1 to SOA.

Acoustic Stimulation↗

PubMed1993

Processing of tactile stimuli and implications for the reading disabled.

A finger localization task was used to investigate interhemispheric transfer of tactile information and the processing of sequential tactile information in 7- and 9-year-old "average" readers and 9-year-old reading disabled boys. The performance of the reading disabled group on interhemispheric transfer and sequential processing was comparable to or worse than the 7-year-old average readers. Significant correlations linked the reading disabled boys' performance on the finger localisation task with their reading skills, performance on perceptual/motor tasks and knowledge of order in the time domain. The results are interpreted in terms of delayed myelination of interhemispheric and intrahemispheric pathways in the reading disabled.

Child↗

PubMed1993

P300 indexes thought disorder in schizophrenics, but allusive thinking in normal subjects.

Loosening of thinking as assessed by the Object Sorting Test (OST) has been found in a percentage of normal subjects but in a higher percentage of schizophrenics, and is familially transmitted in both groups. Loosening of thinking in normal subjects is not associated with evidence of impaired function or increased psychopathology, and in recognition of this, it was termed allusive thinking rather than thought disorder. Both OST-assessed loosening and concreteness of thinking were found to be present independently in a high percentage of schizophrenics, so that both were considered to contribute to schizophrenic thought disorder. The presence of OST-assessed loosening in schizophrenics would, therefore, be predicted to correlate partially rather than totally with measures of schizophrenic thought disorder. It has been suggested that OST-assessed loosening in normal subjects is due to a genetically determined reduction in strength of an inhibitory process that limits the spread of activation of semantic associations and results in a predisposition to schizophrenia. The brain event-related potential P300, which is, in part, under genetic control, may index this inhibitory process. Therefore, it was predicted that in normal subjects, P300 would correlate with OST-assessed loosening of associations. If schizophrenic thought disorder is due to a further weakening of this inhibitory process, it can be predicted that P300 in schizophrenics correlates only weakly with OST-assessed loosening of thinking, but more strongly with schizophrenic thought disorder. In a study in which P300 was elicited using a difficult selective attention task with 15 unmedicated schizophrenics and 22 healthy subjects, all three predictions were supported.

Adult↗

PubMed1993

The effects of between-source discriminability on attended and unattended auditory ERPs.

Event-related potentials (ERPs) for tone pips from attended and unattended sources, which varied on discriminability, were compared with ERPs for the same stimuli recorded during performance of a visual task. This comparison revealed that Nd, the negative shift of attended relative to unattended ERPs, consisted of three components: a negativity in the attended ERP from 100 to 270 ms, a positivity in the unattended ERP from 170 ms to the end of the epoch, and a second negativity in the attended ERP from 270 to 700 ms. In general, the later onset of early Nd with more difficult between-source discriminations could be attributed to the later onset of the positivity in unattended ERPs. A number of hypotheses were advanced for the origin of the unattended positivity: the suppression of the later of two negative components in the 100-220-ms range, an enhanced P2 component, an endogenous positivity, or the resolution of a protracted negativity elicited by preceding attended stimuli.

Adolescent↗