Probing sensory plasticity with rapid forms of motion adaptation
Author
Akyüz, Sibel
Advisor
Kafalıgönül, Hacı Hulusi
Date
2020-09Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
Perception is shaped by both immediate pattern of sensory inputs and previous experience with the external environment. Visual adaptation, a temporary
change in perception following exposure to a stimulus, has been widely employed
to understand how previous sensory experience on different timescales shapes
perception. Visual motion adaptation is a powerful investigative tool to understand sensory plasticity and neural adaptation. However, the neural mechanisms
underlying adaptation induced changes by visual motion are still subject to debate. In the present thesis, spatiotemporal dynamics, neural substrates, and
functional role of sensory plasticity in the human visual system was examined
using rapid forms of motion adaptation paradigm combined with EEG. Specifically, how motion adaption-induced short-term sensory plasticity is reflected at
the neural level and parallel with perceptual performance were explored. Participants were adapted to directional drifting gratings for either short (640 ms
in Experiment 1; 188 ms in Experiments 2 and 3) or long (6.4 s in Experiment
1; 752 ms in Experiments 2 and 3) durations and used a counter-phase flickering (with constant polarity in experiments 1 and 2; polarity inverting within
every step in Experiment 3) grating as a test pattern. Sinusoidal gratings of
phi motion were employed in Experiment 1 whereas; square wave gratings were
used for phi and reverse-phi adaptations in Experiments 2 and 3 to examine how
ON and OFF pathways operate in the visual processing stream. Based on the
EEG analyses in Experiment 1, the scalp sites relevant to motion adaptation
were identified. Experiment 1 showed that both adapting durations led to significant motion aftereffects and EEG results showed that long adaptation produced
stronger aftereffects than the short adaptation condition within 64-112 ms time
range over occipital and parieto-occipital sites. Taken together, these findings
provide important electrophysiological evidence that motion aftereffects reflect
changes in cortical areas mediating low- and mid-level visual motion processing.
They also suggest that adaptation is an active process that involves neural mechanisms operating at different time scales. In Experiments 2 and 3, the short-term
adaptation induced changes over these identified scalp sites were further examined based on Experiment 1. Given that the phi and reverse-phi motion mainly
engage within (ON or OFF) and across (ON and OFF) pathway mechanisms, the
comparisons of adaptation induced changes across these motion types provided
further insights into the nature of corresponding mechanisms over visual cortex.
The behavioral and EEG findings pointed to efficient convergence of information
provided by these pathways and some distinct characteristics of across pathway
mechanisms.
Keywords
Neural adaptationDynamic motion aftereffect
Short-term
Long-term
Event-related potentials
Rapid motion aftereffect
Phi
Reverse-phi
ON-OFF pathways