The Involvement of Superior Frontal Gyri in Perceiving Bistability of Binocular Rivalry and Ambiguous Figure
Date Issued
2007
Date
2007
Author(s)
Liu, Chia-Li
DOI
en-US
Abstract
The function of human visual system is to analyze the input image and to extract
information about objects in the environment. It puzzles investigators for years how
human visual system is capable of reconstructing a stable and coherent
three-dimensional world through two-dimensional retinal information. A collection
of incident lights into our eyes can be interpreted as numerous possible objects, but
most of the time, people are consciously aware of a single percept. It results from a
series of processes and distributed neural networks are implicated to process incoming
visual information. Hence, any impairment among the processes may prevent daily
vision. For instance, macular degeneration causes loss of central vision, which
harms one’s capability to see fine details of an object (Cacho, Dickinson, Reeves, &
Harper, 2007). Damage to unilateral primary visual cortex leads to blindness of the
contralateral visual field (Trevethan, Sahraie, & Weiskrantz, 2007). However, some
patients seemed to exhibit residual visual ability unconsciously, which is called
“blindsight”. Although patients insisted on their visual deficits, some of them
performed better than chance when they were required to guess whether a stimulus
was presented in their blind field (Trevethan et al., 2007). It has raised a lot of
discussion of visual awareness and its neural correlates (Crick & Koch, 1998).
To a normal brain, a stable percept is the best guess given the visual input (Crick
& Koch, 2003). Occasionally, the stable percept may break down. Certain
categories of visual stimuli lead to two or more percepts, rather than one, and those
percepts alternate without any physical changes occurring in the stimulus. This
phenomenon is called “bistable perception” or “multistable perception”, depending on
how many percepts the stimulus evokes (Blake & Logothetis, 2002; Leopold &
9
Logothetis, 1999). Perceptual changes which lack corresponding stimulus changes
offer an opportunity to dissociate perceptual representation from sensory
representation of a stimulus (Moutoussis, Keliris, Kourtzi, & Logothetis, 2005), and
address to the issue of visual awareness (Crick & Koch, 2003).
Ambiguous figure is one type of stimuli which is capable of generating bistable
perception. For example, the famous Necker cube, as Figure 1a shows, can be
perceived as two cubes with different depth features (see Figure 1b & 1c).
Continuously viewing it for a while results in a dynamic sequence of the two cube
percepts. Binocular rivalry is another type of stimuli which also induces bistable
perception. When two discrepant monocular images presented to two eyes
separately, the two images rival for perceptual dominance and only one monocular
image is perceived at a time while the other is suppressed. Figure 2 illustrates an
example of binocular rivalry, in which the two gratings moving in the opposite
directions would lead to perceptual alternations between one and the other.
Although both binocular rivalry and ambiguous figure cause two percepts switching,
they differ in how alternative percepts arise. In the above examples, the Necker cube
needs reorganization of edges, so as to coherently construct it into the other depth, but
different values of a feature, such as motion directions, for two eyes are sufficient to
cause alternative percepts without further grouping.
Subjects
知覺不穩定性
額上回
可逆圖形
視覺
功能性大腦磁振造影
bistable perception
ambiguity
superior frontal gyrus
competition
selection
functional magnetic resonance imaging
Type
other