![]() In the experiments reported below, we started out using an even more controlled local symbol stimulus: a whole-field star–triangle stimulus ( Figure 1c). The stimulus in Figure 1b, consisting of a segmented grating with spatially jittered line orientations, substantially reduces these problems of perceiving where a percept-switch nucleation occurs. This is in accordance with the physiology of interactions between neurons that are organized in orientation columns (Ohki, Chung, Ch'ng, Kara, & Reid, 2005) indeed, the perceptual effect has been quantified psychophysically (Arnold, James, & Roseboom, 2009 Maruya & Blake, 2009 Nichols & Wilson, 2009). This is due to the fact that the new percept propagates relatively fast along a continuous straight line, compared to hopping from one line to the next. Although successive percept alternations occur roughly every 1.5 s, they often appear to start simultaneously along a large part of a line, making it difficult to indicate where they originate. The whole-field pattern of gratings in Figure 1a, used for introductory illustration, turned out to be suboptimal for experimentation. We explore the location and time of initial percept-switch nucleations for homogeneous, unbiased visual fields. A benefit of this stimulus is that elements become larger with eccentricity, thereby taking into account peripheral decreased visibility. (c) A pattern of distinct symbols slows down nucleation-induced phase changes to the extent that all observers are able to keep track of the emerging nucleations. (b) This grating stimulus subtends a smaller retinal area and it contains segments with spatially jittered orientations that slow down nucleation-induced phase changes. A whole-field pattern of gratings can produce quite a few local phase transitions making it challenging to keep track of the number of nucleations. For the other stereo pairs, free fusion suffices. This can be experienced using red–green goggles in the superimposed gratings in the top panel. After several seconds, random nucleations of the green grating break out from suppression through the red pattern. After closing one eye for 3 s (say, the left eye stimulated with the red pattern, and keeping the open eye fixed in the center of the green pattern), flash suppression can be experienced upon opening the left eye: the monocularly viewed (green) pattern is then completely suppressed by the newly visible (red) pattern. A nucleation in binocular rivalry can be regarded as a local phase transition in the state of the neurons associated with the current awareness phase. ![]() The number of nucleations increases with larger images, i.e., by viewing these images from a relatively short distance. (a) When the two eyes view an extended field of orthogonal gratings, the process of binocular rivalry produces continuously emerging percept-switch nucleations of locally dominant red or green domains of differently oriented lines. Collectively, we reveal a governing role of local adaptation in the neurons associated with early visual processing of one eye's image, in the origination of new phases in awareness. Intriguingly, the neuronal processes related to both cross-inhibition and local eye dominance could not predict nucleation probability this is because nucleation inhomogeneity appeared to be different from another previously reported local inhomogeneity known as “onset bias” signifying the local first dominance-choice inhomogeneity upon stimulus onset. ![]() We were able to predict the occurrence probability of the percept nucleations by adaptation buildup of the neurons associated with the representation of one eye's image. We call such spontaneous local breakout an “initial percept-switch nucleation.” We employed homogeneous visual input to examine where, and how, spontaneous local initial percept-switch nucleations originate, demonstrating that their spatial distribution contains locally random inhomogeneities, which are eye- and observer-dependent. Here we focus on the very first spontaneous breakout from the very first suppression phase after onset of the two eyes' competing whole-field stimuli. When the two eyes view incompatible images that subtend the entire visual field, perception alternates between the two images unpredictably: at seemingly random times and locations, observers experience sudden changes in the awareness of the unchanging visual stimulation. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |