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D J O'Boyle

Publications and source records attributed to D J O'Boyle.

15 recordsLinked to original sources
PubMed2004

The contribution of non-ocular response inhibition to visual inhibition of return.

Inhibition of return (IOR) refers to slowed responses to targets presented at the same location as a preceding stimulus. IOR is typically investigated using a cue-target design, in which subjects respond only to the second stimulus of a pair. In such tasks, the measurement of 'true' IOR may be confounded by the effect of non-ocular response inhibition, because the participant must suppress any tendency to respond (e.g. key press) to the first stimulus. This confound may be eliminated using a target-target design, in which responses are made to both stimuli. We assessed the contribution of non-ocular response inhibition to visual IOR, measured in a cue-target task, by testing participants on both cue-target and target-target detection tasks, with identical timings and stimuli. Significant IOR was obtained in both tasks but, at a stimulus onset asynchrony (SOA) of 1400 ms, IOR magnitude was significantly greater in the cue-target condition than in the target-target condition. However, at an SOA of 1800 ms, there was no significant difference in the magnitude of IOR between the two tasks. Thus, a proportion of the total IOR effect observed in visual cue-target tasks can be attributed to non-ocular response inhibition, but this process appears to decay more rapidly than does 'true' IOR, having dissipated by 1800 ms following cue onset.

Adolescent↗
PubMed2002

Effects of a moderate dose of alcohol on simulated laparoscopic surgical performance.

BACKGROUND: In medicine, there is no professional regulation of the drinking of alcohol, nor a body of experimental evidence on which such regulation might be based. Here we report the acute and longer-term ("hangover") effects of a moderate dose of alcohol on performance, as assessed objectively on a laparoscopic surgical simulator. METHODS: In a single-blind, experimental study, medical student subjects were assigned randomly to an alcohol (1.05 mg/kg) or a placebo condition (n = 14 in each). The effects of alcohol on performance on the MIST Virtual Reality surgical simulator were examined 60-90 min and 600-630 min (after a night's sleep) following its ingestion. Measures of the number of errors, time taken, hand movement economy, and excessive use of diathermy were recorded. RESULTS: On each measure, performance was significantly impaired 60-90 min following alcohol ingestion, but there was no hangover effect 600-630 min later, following a night's sleep. This impairment could not be attributed to between-group differences in either predrink performance, expertise or estimated sleep duration during the night preceding the experimental session. CONCLUSIONS: Simulated surgical performance is impaired severely when estimated blood alcohol concentration (BAC) is just above the UK legal limit for driving. These results contribute new, objective and quantitative evidence to the current debate about the use and misuse of alcohol within the medical profession.

Adult↗
PubMed2002

Tactile inhibition of return: non-ocular response inhibition and mode of response.

Inhibition of return (IOR) refers to the slowing of responses to stimuli presented at the same location as a preceding cue. However, the cue-target paradigm used in most previous studies may have overestimated the contribution of eye movement programming to IOR, due to the existence of manual response inhibition effects. This confound can be circumvented by using a target-target paradigm in which participants respond to all stimuli. Here, we compared IOR magnitude from tactile cue-target and target-target tasks involving identical interstimulus intervals of 1,400 and 1,800 ms. Reaction times were measured using a foot pedal toe-lift response and a vocal response. Tactile IOR was observed using both modes of response, demonstrating IOR for the first time using a non-spatial, vocal response. Moreover, IOR effects were significantly smaller in target-target compared to cue-target conditions, thereby confirming the existence of the response inhibition confound.

Adolescent↗
PubMed2002

A sensorimotor theory of temporal tracking and beat induction.

In this paper, we develop a theory of the neurobiological basis of temporal tracking and beat induction as a form of sensory-guided action. We propose three principal components for the neurological architecture of temporal tracking: (1) the central auditory system, which represents the temporal information in the input signal in the form of a modulation power spectrum; (2) the musculoskeletal system, which carries out the action and (3) a controller, in the form of a parieto-cerebellar-frontal loop, which carries out the synchronisation between input and output by means of an internal model of the musculoskeletal dynamics. The theory is implemented in the form of a computational algorithm which takes sound samples as input and synchronises a simple linear mass-spring-damper system to simulate audio-motor synchronisation. The model may be applied to both the tracking of isochronous click sequences and beat induction in rhythmic music or speech, and also accounts for the approximate Weberian property of timing.

Attention↗
PubMed2001

Human locognosic acuity on the arm varies with explicit and implicit manipulations of attention: implications for interpreting elevated tactile acuity on an amputation stump.

In Experiment 1, normal subjects' ability to localize tactile stimuli (locognosia) delivered to the upper arm was significantly higher when they were instructed explicitly to direct their attention selectively to that segment than when they were instructed explicitly to distribute their attention across the whole arm. This elevation of acuity was eliminated when subjects' attentional resources were divided by superimposition of an effortful, secondary task during stimulation. In Experiment 2, in the absence of explicit attentional instruction, subjects' locognosic acuity on one of three arm segments was significantly higher when stimulation of that segment was 2.5 times more probable than that of stimulation of the other two segments. We surmise that the attentional mechanisms responsible for such modulations of locognosic acuity in normal subjects may contribute to the elevated sensory acuity observed on the stumps of amputees.

Adolescent↗
PubMed1999

Proprioceptive regulation of voluntary ankle movements, demonstrated using muscle vibration, is impaired by Parkinson's disease.

OBJECTIVE: To test the hypothesis that the proprioceptive regulation of voluntary movement is disturbed by Parkinson's disease, the effects of experimental stimulation of proprioceptors, using muscle vibration, on the trajectories of voluntary dorsiflexion movements of the ankle joint were compared between parkinsonian and control subjects. METHODS: Twenty one patients with Parkinson's disease, on routine medication (levodopa in all but one), and an equal number of age matched, neurologically intact controls, were trained initially to make reproducible ankle dorsiflexion movements (20 degrees amplitude with a velocity of 9.7 degrees /s) following a visual "go" cue while movement trajectories were recorded goniometrically. During 50% of the experimental trials, vibration (105 Hz; 0.7 mm peak to peak) was applied to the Achilles tendon during the ankle movement to stimulate antagonist muscle spindles; vibrated and non-vibrated trials were interspersed randomly. Subjects' performance was assessed by measuring end point position-that is, the ankle angle attained 2 seconds after the visual "go" cue, from averaged (20 trials) trajectories. RESULTS: Statistical analysis of the end point amplitudes of movement showed that, whereas the amplitudes of non-vibrated movements did not differ significantly between patients with Parkinson's disease and controls, antagonist muscle vibration produced a highly significant reduction in the amplitudes of ankle dorsiflexion movements in both the patient and control groups. However, the extent of vibration induced undershooting produced in the patients with Parkinson's disease was significantly less than that in the controls; the mean vibrated/non-vibrated ratios were 0.86 and 0.54 for, respectively, the patient and control groups. CONCLUSIONS: The present finding of a reduction of vibration induced ankle movement errors in parkinsonian patients resembles qualitatively previous observations of wrist movements, and suggests that Parkinson's disease may produce a general impairment of proprioceptive guidance.

Aged↗
PubMed1996

The accuracy and precision of timing of self-paced, repetitive movements in subjects with Parkinson's disease.

In separate experiments, we studied the temporal accuracy and precision of self-paced, repetitive finger-tapping in two groups of 12 patients with Parkinson's disease and a group of 12 controls matched to the patients with respect to age and general cognitive state. One group (I) of patients was studied initially following 12-15 h abstinence from normal levodopa medication ('off') and again, subsequently, approximately 1 h after ingestion of a single normal dose ('on'). A second group (II) of patients, each of whom had bilaterally asymmetrical neurological signs, was tested using 'worse' and 'better' hands separately. Within each session, subjects were tested repeatedly on a tapping task during which they were required to produce a regular series of self-timed inter-tap intervals, the target duration (550 ms) of which had been established previously during an initial period of tapping in synchrony with the beats of a regular metronome. We employed Wing and Kristofferson's (1973) model of control of motor timing to partition the total variance (TV) about the mean inter-response interval (IRI) produced during the self-paced phase of each run into separate components ['clock' variance (CV) and 'motor-delay' variance (MDV)] attributable to hypothetical 'clock' and 'motor-implementation' processes. Although the mean self-paced IRI of parkinsonian patients was generally shorter than that of controls, only during the 'on' medication condition (Group I) was it significantly so. By comparison with control values, and those observed during the 'on' medication condition, values of TV, CV and MDV in Group I were all significantly higher when subjects were 'off' medication. During the 'on' medication condition, only CV was significantly higher than the control value. In Group II, values of TV, CV and MDV associated with use of the 'worse' hand were all significantly higher than both control values and those associated with use of the 'better' hand. Values of these variables when subjects used the 'better' hand did not, however, differ significantly from control values. The theoretical import of these results is discussed in the light of several important procedural, statistical and computational issues and we conclude that TV, CV, and MDV may all vary significantly as a function of the efficacy of dopaminergic transmission in the basal ganglia.

Aged↗
PubMed1995

Effects of alcohol, at two times of day, on EEG-derived indices of physiological arousal.

Effects of alcohol consumption (0.8 ml/kg) on sleep propensity, spectral characteristics of the EEG and self-rated activation in 16 young male subjects, were investigated during sessions at each of two times of day (08.00 and 16.00). Within-session, time-related changes in the pattern of stage-1 sleep occurrence, and of spectral power in different EEG bands indicated that, irrespective of time of day, physiological arousal increased as estimated blood alcohol concentration (BAC) was rising, and decreased as BAC was falling. Subjective activation was reduced by alcohol during both phases of the BAC curve. A pattern of reduced stage-1 sleep occurrence, higher absolute high alpha power and higher ratings of activation suggested that, irrespective of alcohol condition, physiological and subjective arousal was higher during sessions starting at 16.00 than during those starting at 08.00. There were no significant interactions between alcohol and time of day in respect of any dependent variable. However, the degree to which effects reflecting circadian variation may have been masked by effects of limited sleep restriction prior to morning sessions remains unclear. Subjects reported having slept on only 23.5% of occasions when sleep was scored. Comparison of patterns of statistically significant changes in absolute and relative power in different bands indicated that the two indices do not provide exactly equivalent information about changes in the EEG.

Adult↗
PubMed1995

Effects of alcohol on the sleep-stage structure of a nap in the afternoon.

The effects of the ingestion of 0.8 ml/kg alcohol on the sleep-stage structure of nap sleep were compared with those of a non-alcoholic drink in 8 young male subjects napping between 14.00 h and 15.00 h. During nights immediately preceding experimental sessions, time to bed and time in bed (hence, sleep duration) were controlled. While not affecting total nap sleep duration, alcohol significantly increased time in stage 4 sleep, primarily at the expense of time in stage 2.

Adult↗
PubMed1994

On the efficacy of alcohol placebos in inducing feelings of intoxication.

Placebo efficacy was monitored during three separate experiments concerned with the effects of ethanol (0.8 ml/kg body weight) on some aspect of performance: at regular intervals during experimental sessions, blood alcohol concentration was estimated using a breathalyser and subjects completed an intoxication rating. The simple placebo beverages and manipulations employed were similar to those typically described in the literature, and each experiment involved a repeated measures design. Across the three experiments, maximum mean (median) ratings during placebo sessions, expressed as a percentage of those during alcohol sessions of equivalent period, ranged between 10% (0%) and 69% (72%), and the number of subjects in each experiment for whom a placebo effect was considered to have been negligible ranged between 8% and 73%. For each treatment, intoxication ratings were higher during treatment periods which occurred first than during those which occurred second. However, this transfer effect was twice as large for placebo treatments as for alcohol treatments and, whereas in respect of the latter the effect was statistically non-significant, it was highly significant in respect of the former. The occurrence of such asymmetrical transfer of placebo efficacy suggests that repeated measures designs should be used with caution in drug studies in which a convincing placebo treatment is necessary and difficult to devise.

Adolescent↗
PubMedDate not supplied

Amplitude and fall-time discrimination of unit spike activity using TTL.

An inexpensive and reliable window discriminator simply constructed using TTL integrated circuits is described. The device will discriminate between unit spikes on the basis of amplitude alone or amplitude and fall-time, and simultaneous analysis of two separate spikes is possible. All pulse outputs and amplitude and fall-time windows may be displayed allowing the setting up of window criteria to proceed under direct visual control.

Animals↗