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Biomedical subjects

Michael E R Nicholls

Publications and source records attributed to Michael E R Nicholls.

At least 19 recordsLinked to original sources
PubMed2006

Things that go bump in the right: the effect of unimanual activity on rightward collisions.

Patients with right parietal damage and spatial neglect ignore the leftward features of their environment - causing them to bump into the left-side of doorways. In contrast, the normal population shows a mild attentional bias towards the left. Self-report measures show more collisions to the right in everyday settings. We sought to obtain a quantitative measure of lateralised bumping in a laboratory setting. Participants (n=276) walked through a narrow doorway and the experimenter recorded collisions. To investigate the association between bumping and paper-and-pencil tests of pseudoneglect, a line bisection task was administered. Unilateral activation of the hemispheres has been found to ameliorate the effects of spatial neglect. We investigated the effect of activation by asking participants to move their left-, right- or both-hands as they walked. In the both hands condition, which acted as a baseline, there were more right bumps than left bumps. The rightward bias was exasperated when the left hand moved, presumably because this movement activated the right hemisphere. In contrast, there were more left bumps when the right hand moved. The results demonstrate that bumping is not random and that we collide with the right side more often. Biases in bumping, however, were not related to biases in line bisection. The effect of hand-movement demonstrates that bumping is brought about by an imbalance of activation between the hemispheres.

Adult↗
PubMed2006

Asymmetries for the visual expression and perception of speech.

This study explored asymmetries for movement, expression and perception of visual speech. Sixteen dextral models were videoed as they articulated: 'bat,' 'cat,' 'fat,' and 'sat.' Measurements revealed that the right side of the mouth was opened wider and for a longer period than the left. The asymmetry was accentuated at the beginning and ends of the vocalization and was attenuated for words where the lips did not articulate the first consonant. To measure asymmetries in expressivity, 20 dextral observers watched silent videos and reported what was said. The model's mouth was covered so that the left, right or both sides were visible. Fewer errors were made when the right mouth was visible compared to the left--suggesting that the right side is more visually expressive of speech. Investigation of asymmetries in perception using mirror-reversed clips revealed that participants did not preferentially attend to one side of the speaker's face. A correlational analysis revealed an association between movement and expressivity whereby a more motile right mouth led to stronger visual expressivity of the right mouth. The asymmetries are most likely driven by left hemisphere specialization for language, which causes a rightward motoric bias.

Adolescent↗
PubMed2006

A stimulus-dependent dissociation between the cerebral hemispheres under free-viewing conditions.

Under free-viewing conditions, the leftward stimulus features are frequently overestimated (pseudoneglect). This asymmetry could reflect the operation of: (a) spatial attention mechanisms in the right hemisphere (RH) or, (b) stimulus-specific activation. To test these propositions, we attempted to induce a stimulus-specific dissociation between the hemispheres under free-viewing conditions. In two experiments (n=23, n=22) dextrals carried out two tasks. The 'grayscales' task required luminance judgments between two mirror-reversed luminance gradients. The flicker task required temporal frequency judgments between two mirror-reversed temporal gradients. The grayscales and flicker tasks suited the processing styles of the right and left hemispheres, respectively. For both experiments, a strong leftward bias was observed for the grayscales task, which could be the result of both of the mechanisms outlined above. In Experiment 1, there was a rightward bias for the flicker task-but only for participants with longer reaction times. In Experiment 2, where all responses were delayed, a rightward bias was found for the flicker task for shorter stimuli. The data demonstrate that stimulus-specific dissociations can be induced under free-viewing conditions. However, the fact that the rightward bias was: (a) weaker than the leftward bias and, (b) reduced by increases in length, demonstrates that RH spatial attention mechanisms are also important.

Adolescent↗
PubMed2006

The effect of body and environment-centred coordinates on free-viewing perceptual asymmetries for vertical and horizontal stimuli.

Leftward and upward perceptual biases are commonly reported for horizontal and vertical stimuli, respectively. It is unclear, however, whether these biases are based upon body or environment-centred coordinates. Two experiments examined the contribution of these coordinate systems to free-viewing vertical and horizontal perceptual biases. In Experiment 1, normal participants (n = 35) made forced-choice luminance judgments on two mirror-reversed luminance gradients (the 'greyscales' task) presented in vertical and horizontal orientations. Body and environment-based coordinates were dissociated by tilting participants' heads to the left or right. A leftward and upward bias, which was observed in the horizontal and vertical conditions (respectively) when the head was upright, was extinguished when the head was tilted. Results indicated a dual reliance on body and environmental coordinates with some suggestion that the upward bias was more dependent on environmental coordinates. In Experiment 2 the same stimuli were presented as participants (n = 24) adopted an upright or supine pose. Once again, leftward and upward biases were observed in the upright condition. The leftward bias persisted in the supine condition whereas the upward bias was eliminated. Results demonstrate that the leftward bias is based predominantly on body coordinates whereas the upward bias is reliant on environmental/gravitational coordinates. The possibility that the neural basis for the biases lies in the inter-modal centres of the intraparietal region of the right hemisphere is discussed.

Adolescent↗
PubMed2005

Flexible contrast gain control in the right hemisphere.

This study investigates whether the right hemisphere has more flexible contrast gain control settings for the identification of spatial frequency. Right-handed participants identified 1 and 9 cycles per degree sinusoidal gratings presented either to the left visual field-right hemisphere (LVF-RH) or the right visual field-left hemisphere (RVF-LH). When luminance contrast was randomized across a wide range (20-60%), performance gradually improved with contrast in the LVF-RH. Conversely, performance in the RVF-LH was disrupted and saturated for 20 and 60% of contrast, respectively, leading to a LVF-RH advantage for these contrast levels. When contrast was blocked or randomized for a smaller range (30-50%), the LVF-RH advantage was diminished. Flexible contrast gain control is needed when contrast is randomized across a wide range, but not when it is blocked or randomized across a smaller range. The results therefore suggest that the right hemisphere is able to process spatial frequency information across a wider range of contrast levels than is the left hemisphere.

Adult↗
PubMed2005

Sequential processing in hemispheric word recognition: the impact of initial letter discriminability on the OUP naming effect.

The cerebral hemispheres have been proposed to engage different word recognition strategies: the left hemisphere implementing a parallel, and the right hemisphere, a sequential, analysis. To investigate this notion, we asked participants to name words with an early or late orthographic uniqueness point (OUP), presented horizontally to their left (LVF), right (RVF), or both fields of vision (BVF). Consistent with past foveal research, Experiment 1 produced a robust facilitatory effect of early OUP for RVF/BVF presentations, indicating the presence of sequential processes in lexical retrieval. The effect was absent for LVF trials, which we argue results from the disadvantaged position of initial letters of words presented in the LVF. To test this proposition, Experiment 2 assessed the discriminability of various letter positions in the visual fields using a bar-probe task. The obtained error functions highlighted the poor discriminability of initial letters in the LVF and latter letters in the RVF. To confirm that this asymmetry in initial letter acuity was responsible for the absent OUP effect for LVF presentations, Experiment 3 replicated Experiment 1 using vertical stimulus presentations. Results indicated a marked facilitatory effect of early OUP across visual fields, supporting our contention that the lack of OUP effect for LVF presentations in Experiment 1 resulted from poor discriminability of the initial letters. These findings confirm the presence of sequential processes in both left and right hemisphere word recognition, casting doubt on parallel models of word processing.

Adult↗
PubMed2005

The effect of strategy on pseudoneglect for luminance judgements.

When judging the relative magnitude of the left and right sides of a stimulus, normal participants overestimate the leftward features (pseudoneglect). Although pseudoneglect and clinical neglect operate in opposite directions, the two phenomena may have a common cognitive and neural basis. For neglect, two strategies may be employed when inspecting horizontally aligned stimuli: (1) A global strategy where the stimuli are treated as a gestalt and asymmetries are detected or, (2) a comparison strategy where the qualities on the left and right sides of the stimuli are explicitly compared. To investigate the effect of these strategies on pseudoneglect, normal dextrals (n = 25 and 17) made two-alternative, forced-choice luminance discriminations between two mirror-reversed luminance gradients (greyscales). In an unseparated form, the stimuli are amenable to a global strategy. A comparison strategy was imposed by separating the stimuli into halves (Experiment 1) or quarters (Experiment 2). Despite the fact that the stimuli were equiluminant, participants predominantly chose the stimulus that was dark on the left as being darker overall in the unseparated condition. Response times were also faster for leftward responses. When the stimuli were separated into halves or quarters, the leftward bias was reduced, but not eliminated. The results demonstrate that both strategies contribute to pseudoneglect--though the global strategy may produce stronger pseudoneglect.

Adolescent↗
PubMed2005

Magical ideation and its relation to lateral preference.

Schizophrenia and schizotypal personality have been linked to sinistrality as well as ambidextrality. The current study clarifies the relation between laterality and schizotypal personality by administering a battery of laterality questionnaires to measure hand, eye, ear, and foot preference in a group of 933 university students. To determine whether the relationship between schizotypy and laterality is limited to self-report measures, performance asymmetries between the hands were measured with tapping rate. There was no difference between dextrals and sinistrals in schizotypal personality, as indexed by the Magical Ideation (MI) scale. MI was higher, however, for individuals with a weak preference for either hand or eye compared to those with a strong dominance. In addition, individuals inconsistent in their lateral preference across modalities showed higher MI scores. Performance asymmetries had no effect on MI scores. This lack of effect was attributed to the inability of performance measures, such as tapping rate, to identify ambidextrals. The results support research linking schizotypal personality to ambidextrality and weak cerebral dominance and demonstrate that the association extends to modalities other than hand preference.

Adolescent↗
PubMed2005

Enhanced P1-N1 auditory evoked potential in patients with musicians' cramp.

Auditory evoked potentials (AEPs) were examined in patients with musician's cramp (focal dystonia) in order to determine whether these patients have electrophysiological changes in a sensory system that is not usually associated with symptoms. All participants were professional guitarists and were required to listen to 2,000 monaurally presented stimuli (middle C, with duration of 7 ms). During one block, 250 stimuli were presented to one ear. Once a block was finished, another block was presented in the other ear; in total there were eight blocks of stimuli. During this task, EEGs from 10 scalp electrodes and one bipolar eye channel were continuously recorded. There were no significant latency or topographical differences in the electrophysiological recordings. However, there was a significant group difference in the peak-to-peak amplitude of the P1-N1a component. The patients had a larger peak-to-peak difference than controls (1.63 vs. 0.62 microV). The P1 and N1a are cortically generated potentials. Patients with focal dystonia had an increase in activity compared to controls when processing simple auditory stimuli. Such changes in electrophysiological responses may be a result of increases in excitation or lack of inhibition; alternatively the changes may represent cross-modal maladaptive plasticity from the somatosensory modality to the auditory modality. Thus, this study provides further evidence that patients with focal dystonia have alterations of the central nervous system that are not limited to their symptomatic sensory domain.

Acoustic Stimulation↗
PubMed2005

Hemispheric asymmetry in temporal resolution: contribution of the magnocellular pathway.

Right-handed participants performed simple visual judgments on nonverbal stimuli presented either to the left visual field-right hemisphere (LVF-RH) or to the right visual field-left hemisphere (RVF-LH). The stimuli were exposed for 40-120 msec, followed by a backward mask. When the stimuli were presented against a green background, an RVF-LH advantage was observed for the shortest exposure duration. This result supports the notion that the LH has finer temporal resolution than the RH. Imposition of a red background disrupted performance and eliminated the RVF-LH advantage for the shortest exposure duration. Because the red background attenuates functions of the magnocellular pathway, these results suggest that the magnocellular pathway contributes to the LH advantage for fine temporal resolution.

Attention↗
PubMed2004

The nature and contribution of space- and object-based attentional biases to free-viewing perceptual asymmetries.

Two experiments investigated the contribution of space- and object-based coordinates to previously reported leftward perceptual biases (pseudoneglect) at various locations across visual space. Neurologically intact participants (n = 34 and 27) made luminance discriminations between two left/right mirror-reversed luminance gradients (greyscales task), which were variously displaced around the midline in the participants' left and right hemispaces. The orientations of the stimuli were manipulated so that object- and space-based coordinates were congruent or incongruent. Experiment 1 confirmed the presence of a leftward object-based perceptual bias. The bias was moderated, however, by overattention to the more central stimulus. This central spatial effect could have resulted from the use of task-specific strategies, which were controlled by presenting the stimuli sequentially in Experiment 2. The findings of Experiment 1, a leftward object-based bias and a central spatial bias, were replicated. Overall, the results indicate a leftward object-based bias and a central spatial bias, both of which are relevant for the allocation of attention. The results are discussed with reference to a variety of models of the distribution of attention across space.

Adolescent↗
PubMed2004

Detecting hemifacial asymmetries in emotional expression with three-dimensional computerized image analysis.

Emotions are expressed more clearly on the left side of the face than the right: an asymmetry that probably stems from right hemisphere dominance for emotional expression (right hemisphere model). More controversially, it has been suggested that the left hemiface bias is stronger for negative emotions and weaker or reversed for positive emotions (valence model). We examined the veracity of the right hemisphere and valence models by measuring asymmetries in: (i) movement of the face; and (ii) observer's rating of emotionality. The study uses a precise three-dimensional (3D) imaging technique to measure facial movement and to provide images that simultaneously capture the left or right hemifaces. Models (n = 16) with happy, sad and neutral expressions were digitally captured and manipulated. Comparison of the neutral and happy or sad images revealed greater movement of the left hemiface, regardless of the valence of the emotion, supporting the right hemisphere model. There was a trend, however, for left-sided movement to be more pronounced for negative than positive emotions. Participants (n = 357) reported that portraits rotated so that the left hemiface was featured, were more expressive of negative emotions whereas right hemiface portraits were more expressive for positive emotions, supporting the valence model. The effect of valence was moderated when the images were mirror-reversed. The data demonstrate that relatively small rotations of the head have a dramatic effect on the expression of positive and negative emotions. The fact that the effect of valence was not captured by the movement analysis demonstrates that subtle movements can have a strong effect on the expression of emotion.

Adolescent↗
PubMed2004

An investigation of the relationship between free-viewing perceptual asymmetries for vertical and horizontal stimuli.

Two experiments examine the relationship between free-viewing vertical and horizontal perceptual biases. In Experiment 1, normal participants (n=24) made forced-choice luminance judgments on two mirror-reversed luminance gradients (the 'grayscales' task). The stimuli were presented in vertical, horizontal and oblique (+/-45 degrees ) orientations. Leftward and upward biases were observed in the horizontal and vertical conditions, respectively. In the oblique conditions, leftward and upward biases combined to produce a strong shift of attention away from the lower/right space toward the upper/left. Regression analyses revealed that the oblique biases were the combined product of the vertical and horizontal biases. A lack of correlation between the vertical and horizontal biases, however, suggests they reflect the operation of independent cognitive/neural mechanisms. In Experiment 2, the same stimuli were given to right-hemisphere-lesioned patients with spatial neglect (n=4). Rightward and upward biases were observed for horizontal and vertical stimuli, respectively. The biases combined to produce a strong shift of attention away from the lower/left space toward the upper/right. While our research demonstrates that vertical and horizontal attentional biases are additive, it also appears that they reflect the operation of independent cognitive/neural mechanisms. Potential applications of these findings to the remediation of spatial neglect are discussed.

Adolescent↗
PubMed2004

The greyscales task: a perceptual measure of attentional bias following unilateral hemispheric damage.

The two cerebral hemispheres in humans have been suggested to control contralaterally opposed attentional biases. These biases may be revealed by unilateral hemispheric damage, which often causes contralesional spatial neglect, particularly when the right hemisphere (RH) is affected. Subtle attentional biases have also been observed in normal observers in tasks requiring judgements of horizontal spatial extent, brightness, numerosity and size. Here, we examined attentional biases for judging the darker of two left-right mirror-reversed brightness gradients under conditions of free viewing (the greyscales task). We compared performances of patients with damage to the RH (n=78) and left hemisphere (LH; n=20) with those of normal controls (n=20). Controls showed a small but significant leftward bias, implying a subtle asymmetry favouring the RH. In contrast, RH and LH patients showed extreme rightward and leftward biases, respectively, both of which differed significantly from that of controls. For the patient groups, performance on clinical tests of neglect (cancellation and line bisection) did not predict their greyscales scores. Pathological biases were present in patients without clinical neglect or visual field defects, suggesting that the attentional bias measured by the greyscales task can be dissociated from clinical neglect and visual sensory loss. The greyscales task offers an efficient means of quantifying pathological attentional biases in unilateral lesion patients; it is easy to administer and score, and may be particularly useful for clinical trials of recovery and rehabilitation following stroke.

Adult↗
PubMed2004

Read my lips: asymmetries in the visual expression and perception of speech revealed through the McGurk effect.

It is well known that the right side of the mouth moves more than the left during speech, but little is known about how this asymmetry affects lipreading. We investigated asymmetries in the visual expression and perception of speech using the McGurk effect-an illusion in which incongruent lip movements cause listeners to misreport sounds. Thirty right-handed participants watched film clips in which the left, the right, or neither side of the mouth was covered. The McGurk effect was attenuated when the right side of the mouth was covered, demonstrating that this side is more important to lipreading than is the left side of the mouth. Mirror-reversed images tested whether the asymmetry was the result of an observer bias toward the left hemispace. The McGurk effect was stronger in the normal than in the mirror orientation when the mouth was fully visible. Thus, observers attend more to what they think is the right side of the speaker's mouth. Asymmetries in mouth movements may reflect the gestural origins of language, which are also right lateralized.

Adolescent↗
PubMed2003

Are object- and space-based attentional biases both important to free-viewing perceptual asymmetries?

In contrast to unilateral neglect patients, who overattend to the right hemispace, normal participants attend more to the left: a phenomenon known as pseudoneglect. Two experiments examined whether pseudoneglect results from object- or space-based attentional biases. Normal participants ( n=38, 22) made luminance judgments for two left/right mirror-reversed luminance gradients (greyscales task). The relative lateral position of the greyscales stimuli was manipulated so that object- and space-based coordinates were congruent or incongruent. A baseline condition was also included. A leftward bias, found for the baseline condition, was annulled in the incongruent condition, demonstrating an opposition of object- and space-based biases. The leftward bias was reduced in the congruent condition where object- and space-based biases were expected to be additive. This effect was attributed to extraneous factors, which were avoided in the second experiment by presenting the greyscales stimuli sequentially. Once again, no bias was observed in the incongruent condition where object- and space-based biases were opposed. The leftward bias in the congruent condition was the same as the baseline. The results can be explained by a combination of space- and object-based biases or by space-based biases alone and are discussed with reference to a variety of models, which describe the distribution of attention across space.

Adolescent↗
PubMed2003

Perceptual differences in sequential stimuli across patients with musician's and writer's cramp.

Previous research has demonstrated a relationship between the regularity of motor production and the ability to make accurate perceptual judgments. The current study investigated the temporal abilities of two groups of patients with known movement problems (musicians' and writers' cramp), some of whom have had many years of training in temporal discrimination. Patients and controls (musician and nonmusician, respectively) judged whether the last of six sequential auditory or tactile stimuli occurred earlier or later in comparison to five previously and regularly presented stimuli. In both sensory domains, patients with musicians' cramp detected the early stimulus better than controls. When detecting the onset of late stimuli, only in the auditory domain were patients worse than controls. Patients with writers' cramp, however, did not show any significant group differences in either auditory or tactile domains, suggesting that such patients are not deficient in processing sequential stimuli. In conclusion, compared to controls, patients with musician's cramp demonstrated generalized timing anomalies, occurring in the symptomatic (tactile) and the asymptomatic (auditory) sensory domains. This timing problem is likely to be a consequence of the dystonic symptoms rather than the cause.

Adult↗