INVESTIGADORES
MARTIN Andres
congresos y reuniones científicas
Título:
From Psychophysics to Neural Activity: an Inference about the Motion Pathway in Visual Perception
Autor/es:
MARTÍN, A.; BARRAZA, J. F.
Lugar:
Huerta Grande - Córdoba
Reunión:
Taller; I Reunión Conjunta en Neurociencias (IRCN); 2009
Resumen:
p { margin-bottom: 0.21cm; }
Recently, we showed
that the spatial layout of a stimulus affects our ability to
locate a motion defined boundary. However, this effect does not
appear or is very weak when the task is to discriminate a transparent
stimulus (Martín, Barraza, & Colombo, 2009). Both segmentation
tasks would be performed by V1 and/or V2 cells (Marcar et al., 2000).
In addition, it has been shown that the case of segmentation of
adjacent surfaces would be mediated by a feedback from MT to these
lower areas (Hupe et al., 2001). Because the effect of the spatial
layout would reflect an integrative mechanism occurring in MT such
was proposed by Verghese & Stone, (1997), then we may hypothesize
that the difference between the two kinds of segmentation reported in
our previous work could be due to the fact that transparency is not
mediated by this feedback. In
the case of two adjoining surfaces with different speeds, an
integration process may improve the speed estimation of each surface
by keeping the information of the two different speeds but, in the
case of transparency, an integration in the scale of MT would blend
the local signals and thus, losing the information given by the speed
difference. An alternative hypothesis is that the results are just
reflecting differences in the psychophysical tasks. In
order to disentangle these two alternatives we devised an experiment
in which we test the effect of stimulus layout on speed threshold as
a function of target size. Results show that increasing the angular
distance among patches reduces the speed threshold only for targets
sizes larger than 0.4 deg, which suggests that transparent stimuli
are not affected by the spatial integration occurring after V1/V2.