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Friday October 26th,
2012 from 10:00 to 16:00
Location: Building Maxwell (1st floor A105), UCL Louvain-la-Neuve. Parking Rédimé (see D9 on map).
Program:
10:00 Marcus Missal, Institute of Neuroscience, UCLouvain.
10:45 Coffee break
11:15 Karl Verfaillie, Experimental Psychology, KULeuven.
12:00 Guillaume Masson, Institut de Neurosciences de la Timone, Aix Marseille Université.
12:45 Break
15:00 Sébastien Coppe, ICTEAM Institute and Institute of Neuroscience, UCLouvain. PhD Thesis defense (location: auditorium Barb 92)
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Detailed program: 10:00 Marcus Missal, UCLouvain “Saccadic latency as a window on temporal processing".
Abstract:
Anticipatory eye movements are often evoked by temporal expectation of
an upcoming event. Temporal expectation builds up on the basis of an
implicit estimate of the changing probability of occurrence of an event
(hazard rate). Implicit timing relies on a sense of the passage of time
that is not voluntarily controlled. However, anticipation about when an
event could occur can also be based on an explicit estimate of time on
the basis of information stored in memory. Explicit timing requires
attention. Explicit and implicit timing processes are thought to be
under the control of different neural structures. We tested this
hypothesis by the analysis of the latency of saccades in a paradigm
where movement latency is used as a biomarker of temporal processing.
Indeed, decisions based on different timing processes should lead to
different saccadic latency distributions.Human subjects were required
to make a saccadic eye movement after a delay period that could take
one of four different values randomly (400 ms, 900 ms, 1400 ms and 1900
ms). In the explicit timing experiment, the duration of the delay
period was cued by the previous presentation of a red disk for a
similar duration. In the implicit timing experiment, no temporal
information was provided. We found that during implicit timing of a
target appearance, the latency of saccades with respect to target onset
regularly decreased and more anticipatory saccades were observed for
long delays. This effect was probably due to a perception of the
changing probability of target appearance as time elapsed during the
delay period. During the explicit timing experiments, even more
anticipatory saccades were observed due to the influence of the cue.
Importantly, saccadic latency distributions were different in the
implicit and explicit timing experiments. These results support the
hypothesis of the existence and relative independence of two different
neural systems for timing.
10:45 Coffee break
11:15 Karl Verfaillie, KULeuven
“Transsaccadic object perception.”
Abstract:
Earlier research suggests that transsaccadic memory for objects
involves a relatively sparse, abstract, and categorical representation,
much like visual short-term memory (VSTM) within a fixation. We show
that transsaccadic memory is not restricted to VSTM representations but
that it also includes a maskable, short-lived, and more detailed
epresentation (even for unattended objects), referred to as the
visual analog. The experimental paradigms we developed to demonstrate
this use a combination of blanking, cueing, and masking.
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12:00 Guillaume Masson, Marseille
“Speed processing for tracking eye movements and perception: same or different?”
Abstract:
Moving objects generate motion information at different scales, which
are processed in the visual system with a bank of spatiotemporal
frequency channels. It is not known how the brain pools this
information to reconstruct object speed and whether this pooling is
generic or adaptive; that is, dependent on the behavioral task. We used
rich textured motion stimuli of varying bandwidths to decipher how the
human visual motion system computes object speed in different
behavioral contexts. We found that, although a simple visuomotor
behavior such as short-latency ocular following responses takes
advantage of the full distribution of motion signals, perceptual speed
discrimination is impaired for stimuli with large bandwidths. Such
opposite dependencies can be explained by an adaptive gain control
mechanism in which the divisive normalization pool is adjusted to meet
the different constraints of perception and action. 12:45 Break 15:00 Sébastien Coppe, UCLouvain
“Experimental and theoretical approaches to predictive eye movements”
Abstract:
This thesis
focuses on the pursuit eye movements, which are required to track a moving object.
In particular, predictive eye movements will be analyzed in order to better
understand their mechanisms and the way they interact with visual information.
Two different approaches are used to achieve this purpose. First, a theoretical
approach consists in modeling the pursuit system, by simulating experimental
data and by making hypotheses on the oculomotor behavior. This approach is then
supplemented and combined with experimental studies. These behavioral studies
were performed on normal subjects, but also on patients with some type of
dementia, showing the importance of the frontal lobes for the predictive
pursuit eye movements.
The thesis illustrates
the fact that both theoretical and experimental approaches are complementary
and that each of them gives valuable information to the other.
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last update: October 10th, 2012
Author: Philippe LEFEVRE
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