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Talgar, C.P. & Carrasco,
M. (2002). Vertical meridian asymmetry in spatial resolution: Visual and
attentional factors. Psychonomic Bulletin & Review, 9(4): 714-722..
Abstract
We investigated whether spatial resolution would be the same in the lower
and upper halves of the vertical meridian (VM) of our visual field
and whether attention would affect them differentially. It has been reported
that (1) attending to the target's location improves performance in a
texture segregation task when the observer's spatial resolution is too
low (peripheral locations) but impairs it when resolution is already too
high (central locations) for the task. This finding indicates an enhanced
spatial resolution at the attended location (Yeshurun & Carrasco,
1998 2000), (2) observers' contrast sensitivity is higher in the lower
than in the upper VM, a phenomenon known as vertical meridian asymmetry
(VMA), an asymmetry determined by visual rather than by attentional factors
(Carrasco, Talgar, & Cameron, 2001). In the present texture segregation
task, performance was assessed under neutral- and peripheral- cue conditions.
Transient covert attention was systematically manipulated by using a peripheral
cue that indicated the target's location and its onset. Observers reported
the interval containing a target patch appearing at one of a number of
eccentricities in a large texture pattern along the VM. We found that
(1) performance peaked at farther eccentricities in the lower than in
the upper visual VM, indicating that resolution was higher in the lower
half, and (2) the peripheral cue affected performance along the VM uniformly,
indicating that the degree of enhanced resolution brought about by transient
attention was constant along the VM. Thus, we conclude that the VMA for
spatial resolution is determined by visual, not transient covert attentional,
constraints.
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