Biomedical subjects

Robert J Snowden

Publications and source records attributed to Robert J Snowden.

21 records · Page 2Linked to original sources

PubMed2002

Spatial shifts in visual attention in normal ageing and dementia of the Alzheimer type.

Using a spatial-cueing paradigm, we assessed the ability of Alzheimer's disease patients, age-matched controls and younger participants to use cues to guide attention to the location indicated by the cue. In separate experiments, we attempted to isolate cues that attract attention automatically (exogenous cueing) and those that require the wilful movement of attention (endogenous cues). We found significant cueing effects for all three groups of participants for both types of cue. However, the group with Alzheimer's disease showed far greater cueing effects when using an exogenous cue, whilst no difference between group's ability to use the cue was found for the endogenous cue. No differences in cueing were found for either cue type as a function of normal ageing. We further tested whether the differences in cueing found in the group with Alzheimer's disease was due to a generalised slowing of function. After transforming the data to take account of the overall slowing of all responses in this group, we still found significant differences between this group and the control groups. We conclude that patients with Alzheimer's disease have an abnormality in automatic, but not controlled visuospatial attention.

Aged↗

PubMed2002

Visual attention to color: parvocellular guidance of attentional resources?

Although transient changes in luminance have been well documented to automatically attract attention to their location, experiments looking at abrupt changes in color have failed to find similar attentional capture. These results are consistent with current theories of the role of the magnocellular (M) and parvocellular (P) streams that postulate that the M stream, which is "color-blind," plays the dominant role in guiding attention and eye movements. The experiment reported here used stimuli that contained only information defined by color, and masked residual luminance information with dynamic noise, to assess the capacity of purely chromatic cues to automatically guide spatial attention. Such stimuli were as effective as those containing large luminance signals in guiding attention. To the extent that these purely chromatic signals isolated the P stream, these results suggest that this stream is also capable of automatic attentional capture. Hence, color vision not only aids target identification but also is a strong aid for target detection and localization.

Adult↗

PubMed2002

Which schizotypal dimensions abolish latent inhibition?

OBJECTIVE: To evaluate which dimensions of schizotypy are associated with a reduction in latent inhibition (LI), akin to that seen in schizophrenia. DESIGN: LI was compared in low and high scorers on the four dimensions of the OLIFE questionnaire (Mason, Claridge, & Jackson, 1995), with the predictions that the unusual experiences and impulsive non-conformity subscales would be associated with loss of LI, while the introvertive anhedonia subscale would not be. METHODS: A total of 80 healthy volunteers completed a visual LI task. Half of these participants were pre-exposed to the conditioning stimulus; the others were not. The primary outcome measure was the number of trials taken to learn the task. RESULTS: LI was reduced for the dimensions of unusual experiences, impulsive non-conformity and cognitive disorganization. There was no effect of introvertive anhedonia. The effect of unusual experiences and impulsive non-conformity upon LI was mediated via changes in the pre-exposure group and not in the non-pre-exposed group. Conversely, high scorers on the cognitive disorganization scale showed slower learning in non-pre-exposure, but with no effect upon stimulus pre-exposure. As the unusual experiences and implusive non-conformity scales were correlated, we examined if either of these was primary. Analysis showed unusual experiences to be primary, with impulsive non-conformity not contributing significant additional independent variance. CONCLUSIONS: Our results support the proposition that the cognitive processes underlying the mediation of LI are related to the genesis of unusual experiences in schizotypy and, by extension, the positive symptoms of schizophrenia.

Adolescent↗