PubMed Health⌕ Search

Biomedical subjects

S J Hevenor

Publications and source records attributed to S J Hevenor.

5 recordsLinked to original sources
PubMed2000

The effect of variability of unattended information on global and local processing: evidence for lateralization at early stages of processing.

Visual objects can often be analyzed as hierarchical in structure, composed of local elements that are spatially arranged to form a global shape. The brain mechanisms involved in the analysis of hierarchical figures have been under considerable scrutiny in recent years, and one of the many interesting features that have emerged is that there is an asymmetry across the two hemispheres for global (right hemisphere) vs local (left hemisphere) processing. Event-related potentials (ERP) were used to examine selective attention to global or local levels of hierarchical figures to determine the stage of processing at which the asymmetry first emerges. Two conditions were tested, one in which unattended information was variable from trial to trial, and one in which it was not. The variability of unattended information influenced the lateralization of processing. Presentation of invariable, neutral distractors resulted in global/local processing asymmetries at early stages (P1). In contrast, presentation of variable, task-relevant distractors resulted in processing asymmetries that occurred at much later stages (N2). Our hypothesis is that lateralized enhancement of neural populations in extrastriate cortex results from both selective attention to locations in the visual field, as well as selective attention to global or local information. We suggest that unattended information that varies from trial to trial is processed in parallel with attended information, masking hemisphere biases for local vs global information at early stages of processing.

Adult↗
PubMed1999

Using mismatch negativity to measure auditory temporal resolution thresholds.

It has been hypothesized that poor auditory temporal resolution is related to language-learning problems in children as well as problems with speech perception in noise in the elderly. We show that the presence of occasional silent gaps between short tone pips elicits mismatch negativity (MMN) in young adults. We also measured gap-detection thresholds with MMN that agree well with behavioural thresholds. Near threshold, the MMN increases as the gap size increases millisecond by millisecond. The MMN methodology for measuring temporal resolution is not only robust, but can be applied identically across the life span as it does not require the attention of participants or a behavioural response. We are now in a position to examine temporal resolution in infancy.

Acoustic Stimulation↗
PubMed1996

Amphetamine disrupts negative patterning but does not produce configural association deficits on an alternative task.

Three experiments investigated the effects of d-amphetamine on the performance of rats on tasks that required the discrimination of configural cues (i.e., those in which two stimulus elements, tone and light, have a meaning when presented together that is distinct from the meaning of the same elements presented in isolation from each other). In a negative patterning task (Experiment 1), rats were trained in a GO/NO-GO task in which either stimulus alone signalled reward availability whilst the compound did not. Amphetamine (0.5, 1.0 and 2.0 mg/kg) was found to disrupt performance by increasing responses to the unrewarded compound. Responses were also increased during the ITI. In contrast, in Experiments 2 and 3 amphetamine had little impact on performance on a task in which the rats had to respond to either of the single stimuli with one response (lever-press or chain-pull) and to the compound stimulus with the other response. The results add credence to the suggestion of Davidson et al. (Behav. Neurosci., 1993, 107, 227-234) that hippocampal lesions disrupt negative patterning by increasing responsiveness rather than by disrupting a configural association system and do not support the idea that increased dopamine activity disrupts configural associations. The findings are discussed in the context of hippocampal-dopamine interactions.

Animals↗