Biomedical subjects

David I Shore

Publications and source records attributed to David I Shore.

13 recordsLinked to original sources

PubMed2006

Global-local visual processing in high functioning children with autism: structural vs. implicit task biases.

Global-local processing was examined in high-functioning children with autism and in groups of typically developing children. In experiment 1, the effects of structural bias were tested by comparing visual search that favored access to either local or global targets. The children with autism were not unusually sensitive to either level of visual structure. In experiment 2 a structural global bias was pitted against an implicit task bias favoring the local level. Children with autism were least sensitive to the structural global bias but showed greater sensitivity to the implicit task bias. This suggests that autism is associated with differences in the executive control processes used to guide attention to either the global or local level, and strategies may be more "data driven".

Attention↗

PubMed2006

The development of change detection.

Changes to a scene often go unnoticed if the objects of the change are unattended, making change detection an index of where attention is focused during scene perception. We measured change detection in school-age children and young adults by repeatedly alternating two versions of an image. To provide an age-fair assessment we used a bimanual choice rather than open-ended verbal responses. The difference in detection speed and accuracy between 50-ms versus 250-ms blank screens between views indexed change detection in short-term visual memory independent of sensory and response processes. Younger children were significantly less efficient than older participants, especially when an object changed color or had a part deleted. Changes in object orientation were detected more readily. These results point to important differences in the perceptual reality of younger and older children.

Adolescent↗

PubMed2005

Temporal aspects of the visuotactile congruency effect.

We report an experiment designed to investigate the temporal dynamics of the visuotactile crossmodal congruency effect. Vibrotactile targets were presented randomly to the index finger (top side of a hand-held cube) or thumb (bottom side) of either hand while visual distractors were presented randomly from one of the same four possible locations. The stimulus onset asynchrony (SOA) between the vibrotactile target and the visual distractor was varied on a trial-by-trial basis. Participants made speeded discrimination responses regarding the elevation of the vibrotactile targets (i.e., upper versus lower) while trying to ignore the visual distractors. The largest crossmodal congruency effects (defined as the difference in performance between incongruent and congruent elevation distractor trials) were obtained when the visual distractor preceded the vibrotactile target by 50-100 ms, although significant effects were also reported when the distractor followed the target by as much as 100 ms. These results are discussed in terms of the conjoint influence of response competition, crossmodal perceptual interactions (i.e., the ventriloquism effect), and exogenous spatial attention on the crossmodal congruency effect. The distinct temporal signatures of each of these effects are also highlighted.

Adult↗

PubMed2005

Integration of visual and tactile stimuli: top-down influences require time.

In a visuotactile congruency task, a distracting flash of light presented near a tactile target can influence speeded judgments of tactile location. Localization of the tactile target is more rapid when the elevation of the visual distractor is congruent with the tactile stimulus than when it is incongruent. The goal of the present study was to examine the degree of control that can be exerted on the process proposed to integrate the visual and tactile stimuli. To this end, the proportion of spatially congruent items was manipulated across blocks of trials. A robust congruency effect was observed across three experiments. There was no effect of proportion congruency (varied between 75 and 11% congruent) when the visual event was presented only 30 ms prior to the tactile event. When this lead-time was increased to 100 ms there was a significant increase in the congruency effect, for errors, in the high proportion congruent conditions (experiment 3). We conclude that with sufficient lead-time, top-down influence can be exerted in this task, however, when presented at near simultaneity, visuotactile integration is independent of top-down effects.

Adult↗

PubMed2005

Audiovisual prior entry.

It is almost one hundred years since Titchener [E.B. Titchener, Lectures on the Elementary Psychology of Feeling and Attention, Macmillan, New York, 1908] published his influential claim that attending to a particular sensory modality (or location) can speed up the relative time of arrival of stimuli presented in that modality (or location). However, the evidence supporting the existence of prior entry is, to date, mixed. In the present study, we used an audiovisual simultaneity judgment task in an attempt to circumvent the potential methodological confounds inherent in previous research in this area. Participants made simultaneous versus successive judgment responses regarding pairs of auditory and visual stimuli at varying stimulus onset asynchronies (SOAs) using the method of constant stimuli. In different blocks of trials, the participants were instructed to attend either to the auditory or to the visual modality, or else to divide their attention equally between the two modalities. The probability of trials containing intramodal stimulus pairs (e.g., vision-vision or audition-audition) was increased in the focused attention blocks to encourage participants to follow the instructions. The perception of simultaneity was modulated by this attentional manipulation: Visual stimuli had to lead auditory stimuli by a significantly smaller interval for simultaneity to be perceived when attention was directed to vision than when it was directed to audition. These results provide the first unequivocal evidence for the existence of audiovisual prior entry.

Acoustic Stimulation↗

PubMed2005

Spatial modulation of tactile temporal-order judgments.

We report a series of three experiments designed to examine the effect of posture on tactile temporal processing. Observers reported which of two tactile stimuli, presented to the left and right index fingers (experiments 1-3; or thumb, experiment 3), was perceived first while adopting one of two postures--hands-close (adjacent, but not touching) or hands-far (1 m apart)--in the dark. Just-noticeable differences were significantly smaller in the hands-far posture across all three experiments. In the first two experiments we compared hand versus foot responses and found equivalent advantages for the hands-far posture. In the final experiment the stimuli were presented to either the same or different digit on each hand (index finger or thumb) and we found that only when the same digit on each hand was stimulated was there an advantage for the hands-far posture. The finding that temporal precision was better with greater distance contradicts predictions based on attention-switching models of temporal-order judgments, and also contrasts with results from similar experimental manipulations in other modalities (eg vision). These results provide support for a rapid and automatic process that transforms the representation of a tactile stimulus from a skin-centred reference frame to a more external (eg body-centred or allocentric) one.

Adult↗

PubMed2005

Audio-visual simultaneity judgments.

The relative spatiotemporal correspondence between sensory events affects multisensory integration across a variety of species; integration is maximal when stimuli in different sensory modalities are presented from approximately the same position at about the same time. In the present study, we investigated the influence of spatial and temporal factors on audio-visual simultaneity perception in humans. Participants made unspeeded simultaneous versus successive discrimination responses to pairs of auditory and visual stimuli presented at varying stimulus onset asynchronies from either the same or different spatial positions using either the method of constant stimuli (Experiments 1 and 2) or psychophysical staircases (Experiment 3). The participants in all three experiments were more likely to report the stimuli as being simultaneous when they originated from the same spatial position than when they came from different positions, demonstrating that the apparent perception of multisensory simultaneity is dependent on the relative spatial position from which stimuli are presented.

Adult↗

PubMed2004

Audiotactile temporal order judgments.

We report a series of three experiments in which participants made unspeeded 'Which modality came first?' temporal order judgments (TOJs) to pairs of auditory and tactile stimuli presented at varying stimulus onset asynchronies (SOAs) using the method of constant stimuli. The stimuli were presented from either the same or different locations in order to explore the potential effect of redundant spatial information on audiotactile temporal perception. In Experiment 1, the auditory and tactile stimuli had to be separated by nearly 80 ms for inexperienced participants to be able to judge their temporal order accurately (i.e., for the just noticeable difference (JND) to be achieved), no matter whether the stimuli were presented from the same or different spatial positions. More experienced psychophysical observers (Experiment 2) also failed to show any effect of relative spatial position on audiotactile TOJ performance, despite having much lower JNDs (40 ms) overall. A similar pattern of results was found in Experiment 3 when silent electrocutaneous stimulation was used rather than vibrotactile stimulation. Thus, relative spatial position seems to be a less important factor in determining performance for audiotactile TOJ than for other modality pairings (e.g., audiovisual and visuotactile).

Acoustic Stimulation↗

PubMed2003

Audiovisual temporal order judgments.

In two experiments, we examined the extent to which audiovisual temporal order judgments (TOJs) were affected by spatial factors and by the dimension along which TOJs were made. Pairs of auditory and visual stimuli were presented from either the left and/or right of fixation at varying stimulus onset asynchronies (SOAs), and participants made unspeeded TOJs regarding either "Which modality was presented first?" (experiment 1), or "Which side was presented first?" (experiment 2). Modality TOJs were more accurate (i.e. just-noticeable differences, JNDs, were smaller) when the auditory and visual stimuli were presented from different spatial positions rather than from the same position, highlighting an important potential confound inherent in previous research. By contrast, spatial TOJs were unaffected by whether or not the two stimuli were presented in different modalities. A between-experiments comparison revealed more accurate performance (i.e. smaller JNDs) when people reported which modality came first than when they reported which side came first for identical bimodal stimulus pairs. These results demonstrate that multisensory TOJs are critically dependent on both the relative spatial position from which stimuli are presented and on the particular dimension being judged.

Acoustic Stimulation↗

PubMed2003

Multisensory temporal order judgments: the role of hemispheric redundancy.

Participants made unspeeded 'Which modality came first?' temporal order judgments (TOJs) in response to pairs of auditory and visual stimuli presented at varying stimulus onset asynchronies (SOAs), using the method of constant stimuli. The presentation of auditory and visual stimuli from different spatial positions facilitated performance (i.e. just noticeable differences were lowered) only when the stimuli were presented across the body midline (Experiment 4), but not when both stimuli were either placed on the body midline (Experiments 1-3), or else within the same hemifield (Experiment 5). These results demonstrate that hemispheric redundancy may account for the facilitatory effects reported in previous multisensory TOJs research when stimuli were presented from different spatial locations. Our results also show that the accuracy with which people can make multisensory TOJs is unaffected by the predictability of target stimulus locations, suggesting little role for spatial attention in this aspect of multisensory temporal perception.

Acoustic Stimulation↗

PubMed2003

Multisensory representation of limb position in human premotor cortex.

Using functional magnetic resonance imaging (fMRI) in humans, we identified regions of cortex involved in the encoding of limb position. Tactile stimulation of the right hand, across the body midline, activated the right parietal cortex when the eyes were closed; activation shifted to a left parietofrontal network when the eyes were open. These data reveal important similarities between human and non-human primates in the network of brain areas involved in the multisensory representation of limb position.

Brain Mapping↗

PubMed2003

Multisensory temporal order judgments: when two locations are better than one.

In Experiment 1, participants were presented with pairs of stimuli (one visual and the other tactile) from the left and/or right of fixation at varying stimulus onset asynchronies and were required to make unspeeded temporal order judgments (TOJs) regarding which modality was presented first. When the participants adopted an uncrossed-hands posture, just noticeable differences (JNDs) were lower (i.e., multisensory TOJs were more precise) when stimuli were presented from different positions, rather than from the same position. This spatial redundancy benefit was reduced when the participants adopted a crossed-hands posture, suggesting a failure to remap visuotactile space appropriately. In Experiment 2, JNDs were also lower when pairs of auditory and visual stimuli were presented from different positions, rather than from the same position. Taken together, these results demonstrate that people can use redundant spatial cues to facilitate their performance on multisensory TOJ tasks and suggest that previous studies may have systematically overestimated the precision with which people can make such judgments. These results highlight the intimate link between spatial and temporal factors in determining our perception of the multimodal objects and events in the world around us.

Adult↗

PubMed2002

Confusing the mind by crossing the hands.

Observers made temporal order judgements (TOJs) regarding which of two tactile stimuli presented to either hand (at stimulus onset asynchronies of up to 200 ms) occurred first. When the observers' hands were placed in an uncrossed posture (i.e., each hand in its own hemispace), performance was accurate, with a just noticeable difference (JND; the smallest interval which produces 75% correct performance) of 34 ms. By contrast, when the hands were crossed over the midline, performance declined such that 124 ms was needed for accurate performance. In a second experiment, we presented visual instead of tactile stimuli to evaluate the relative contribution of motor and perceptual confusions to the effect. While performance with crossed hands was significantly worse than with uncrossed hands (JND=36 vs. 31 ms, respectively), this difference was negligible compared to that with tactile stimuli. In a third experiment, experienced observers showed a robust crossed-hands deficit which was not improved by using different fingers on either hand. We argue that the decline in tactile discrimination performance when the hands are crossed reflects a failure to represent appropriately near simultaneous bimanual tactile stimuli, and stands in marked contrast to many recent observations of efficient remapping of singly-presented tactile stimuli.

Analysis of Variance↗