Abstract
The visual system is constantly bombarded with information originating from the outside world, but it is unable to process all the received information at any given time. In fact, the most salient parts of the visual scene are chosen to be processed involuntarily and immediately after the first glance along with endogenous signals in the brain. Vision scientists have shown that the early visual system, from retina to lateral geniculate nucleus (LGN) and then primary visual cortex, selectively processes the low-level features of the visual scene. Everything we perceive from the visual scene is based on these feature properties and their subsequent combination in higher visual areas. Different experiments have been designed to investigate the impact of these features on saliency and understand the relative visual mechanisms. In this paper, we review the psychophysical experiments which have been published in the last decades to indicate how the low-level salient features are processed in the early visual cortex and extract the most important and basic information of the visual scene. Important and open questions are discussed in this review as well and one might pursue these questions to investigate the impact of higher level features on saliency in complex scenes or natural images.
Highlights
The visual cortex is constantly processing the information coming from the outside world as well as endogenous signals originating from higher brain levels
Feature Saliency Tasks: Psychophysical Experiments process of focusing on a part of the visual scene in the center of gaze, within the high acuity fovea which has a high density of photoreceptors, or covertly attending at the locations away from the center of gaze, where visual resolution is low
Selective attention allows us to tune out the unimportant visual information and focus on what information really matters which is embedded in the salient part(s) of the scene (Wolf and Horowitz, 2004; Carrasco, 2011)
Summary
The visual cortex is constantly processing the information coming from the outside world as well as endogenous signals originating from higher brain levels. A research study has simultaneously compared the response time of the saliency effect of two competitive targets which were presented against the regular orientation lines in a pattern on the background (Nothdurft, 2000b) In this visual task, a test and a reference bar target were randomly placed on each side of the fixation point (the left or right of the visual field). Nothdurft (2000c) reported that orientation and motion saliency are more detectable in medium density rather than low and high densities This was postulated after presenting a regular line array in which the density of lines in the left half was different from the right one while asking the subjects to specify the most salient part. How do they compete when two images with different salient parts are presented to each eye separately? What if we show salient items with different temporal resolution, for example, an image with orientation contrast to one eye and an image with color contrast to another eye? How does information from the eyes bind together in this case? Can saliency detection at the monocular level affect which eye will be dominant? Using an eye tracker to record the subject’s eye movements during similar experiments is useful to analyze unconscious reaction of the eyes after presenting different images to each eye
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