Saccadic suppression of image displacement (SSID) is the phenomenon in visual perception where the brain selectively blocks visual processing during eye movements in such a way that large changes in object location in the visual scene during a saccade or blink are not detected.
The phenomenon described by Bridgeman et al. (Bridgeman, G., Hendry, D., & Stark, L., 1975) is characterized by the inability to detect changes in the location of a target when the change occurs immediately before, during, or shortly after the saccade, following a time course very similar to that of the suppression of visual sensitivity, with a magnitude perhaps even more striking than that of visual sensitivity (4 log units vs. 0.5–0.7 log units (Bridgeman et al., 1975; Volkmann, 1986)).
These results indicate that the human perceptual system neglects many useful pieces of information when it comes to spatially localizing target displacements occurring during a saccade. Surprisingly, in contrast to the perceptual system, the motor system is able to access precise spatial information in order to render precise motor actions during a saccade (Bridgeman, Lewis, Heit, & Nagle, 1979; Prablanc & Martin, 1992).
If a target which is displaced during a saccade is not present at the end of the saccade, but reappears a short time later after a blank interval, subjects are able to regain the ability to successfully detect whether the target has moved. In these studies it was discovered that as the gap between the end of the saccade and the presentation of the shifted target increases, subjects become much more accurate at detecting displacement, and that with a gap of 150 ms participants had reached ceiling in their performance. Deubel and colleagues termed this the 'blanking effect' (Deubel et al., 1996; Deubel et al., 2004).
These results suggest that while extra-retinal information is present, and contains accurate localization information, it is only used when other information is not available – specifically retinal scene information. According to this model, three sources of information must be present in order to maintain visual constancy and successfully determine the direction of a target displacement: the target position prior to the saccade, extra retinal information, and a retinal error signal from the corrective saccade to determine the actual direction of target movement by comparing it to the efference copy and proprioceptive inflow (Deubel et al., 1996).
Using the device pictured on the right, Ziat et al. (2010) demonstrated a phenomenon akin to the saccadic suppression of image displacement (Bridgeman et al., 1975) in the tactile system. Under certain conditions participants failed to detect that dots had changed location as they moved their fingers over the tactile display.
A saccade is a quick, simultaneous movement of both eyes between two or more phases of fixation in the same direction. In contrast, in smooth pursuit movements, the eyes move smoothly instead of in jumps. The phenomenon can be associated with a shift in frequency of an emitted signal or a movement of a body part or device. Controlled cortically by the frontal eye fields (FEF), or subcortically by the superior colliculus, saccades serve as a mechanism for fixation, rapid eye movement, and the fast phase of optokinetic nystagmus. The word appears to have been coined in the 1880s by French ophthalmologist Émile Javal, who used a mirror on one side of a page to observe eye movement in silent reading, and found that it involves a succession of discontinuous individual movements.
Saccadic masking, also known as (visual) saccadic suppression, is the phenomenon in visual perception where the brain selectively blocks visual processing during eye movements in such a way that neither the motion of the eye nor the gap in visual perception is noticeable to the viewer.
Iconic memory is the visual sensory memory register pertaining to the visual domain and a fast-decaying store of visual information. It is a component of the visual memory system which also includes visual short-term memory (VSTM) and long-term memory (LTM). Iconic memory is described as a very brief, pre-categorical, high capacity memory store. It contributes to VSTM by providing a coherent representation of our entire visual perception for a very brief period of time. Iconic memory assists in accounting for phenomena such as change blindness and continuity of experience during saccades. Iconic memory is no longer thought of as a single entity but instead, is composed of at least two distinctive components. Classic experiments including Sperling's partial report paradigm as well as modern techniques continue to provide insight into the nature of this SM store.
The superior colliculus is a structure lying on the roof of the mammalian midbrain. In non-mammalian vertebrates the homologous structure, is known as the optic tectum or optic lobe. The adjective form tectal is commonly used for both structures.
Multisensory integration, also known as multimodal integration, is the study of how information from the different sensory modalities may be integrated by the nervous system. A coherent representation of objects combining modalities enables animals to have meaningful perceptual experiences. Indeed, multisensory integration is central to adaptive behavior because it allows animals to perceive a world of coherent perceptual entities. Multisensory integration also deals with how different sensory modalities interact with one another and alter each other's processing.
Change blindness is a perceptual phenomenon that occurs when a change in a visual stimulus is introduced and the observer does not notice it. For example, observers often fail to notice major differences introduced into an image while it flickers off and on again. People's poor ability to detect changes has been argued to reflect fundamental limitations of human attention. Change blindness has become a highly researched topic and some have argued that it may have important practical implications in areas such as eyewitness testimony and distractions while driving.
Microsaccades are a kind of fixational eye movement. They are small, jerk-like, involuntary eye movements, similar to miniature versions of voluntary saccades. They typically occur during prolonged visual fixation, not only in humans, but also in animals with foveal vision. Microsaccade amplitudes vary from 2 to 120 arcminutes. The first empirical evidence for their existence was provided by Robert Darwin, the father of Charles Darwin.
Smooth pursuit eye movements allow the eyes to closely follow a moving object. It is one of two ways that visual animals can voluntarily shift gaze, the other being saccadic eye movements. Pursuit differs from the vestibulo-ocular reflex, which only occurs during movements of the head and serves to stabilize gaze on a stationary object. Most people are unable to initiate pursuit without a moving visual signal. The pursuit of targets moving with velocities of greater than 30°/s tends to require catch-up saccades. Smooth pursuit is asymmetric: most humans and primates tend to be better at horizontal than vertical smooth pursuit, as defined by their ability to pursue smoothly without making catch-up saccades. Most humans are also better at downward than upward pursuit. Pursuit is modified by ongoing visual feedback.
Supplementary eye field (SEF) is the name for the anatomical area of the dorsal medial frontal lobe of the primate cerebral cortex that is indirectly involved in the control of saccadic eye movements. Evidence for a supplementary eye field was first shown by Schlag, and Schlag-Rey. Current research strives to explore the SEF's contribution to visual search and its role in visual salience. The SEF constitutes together with the frontal eye fields (FEF), the intraparietal sulcus (IPS), and the superior colliculus (SC) one of the most important brain areas involved in the generation and control of eye movements, particularly in the direction contralateral to their location. Its precise function is not yet fully known. Neural recordings in the SEF show signals related to both vision and saccades somewhat like the frontal eye fields and superior colliculus, but currently most investigators think that the SEF has a special role in high level aspects of saccade control, like complex spatial transformations, learned transformations, and executive cognitive functions.
The gaze-contingency paradigm is a general term for techniques allowing a computer screen display to change in function depending on where the viewer is looking. Gaze-contingent techniques are part of the eye movement field of study in psychology.
Flash suppression is a phenomenon of visual perception in which an image presented to one eye is suppressed by a flash of another image presented to the other eye.
Extinction is a neurological disorder that impairs the ability to perceive multiple stimuli of the same type simultaneously. Extinction is usually caused by damage resulting in lesions on one side of the brain. Those who are affected by extinction have a lack of awareness in the contralesional side of space and a loss of exploratory search and other actions normally directed toward that side.
Perceptual learning is learning better perception skills such as differentiating two musical tones from one another or categorizations of spatial and temporal patterns relevant to real-world expertise as in reading, seeing relations among chess pieces, knowing whether or not an X-ray image shows a tumor.
Amorphosynthesis, also called a hemi-sensory deficit, is a neuropsychological condition in which a patient experiences unilateral inattention to sensory input. This phenomenon is frequently associated with damage to the right cerebral hemisphere resulting in severe sensory deficits that are observed on the contralesional (left) side of the body. A right-sided deficit is less commonly observed and the effects are reported to be temporary and minor. Evidence suggests that the right cerebral hemisphere has a dominant role in attention and awareness to somatic sensations through ipsilateral and contralateral stimulation. In contrast, the left cerebral hemisphere is activated only by contralateral stimuli. Thus, the left and right cerebral hemispheres exhibit redundant processing to the right-side of the body and a lesion to the left cerebral hemisphere can be compensated by the ipsiversive processes of the right cerebral hemisphere. For this reason, right-sided amorphosynthesis is less often observed and is generally associated with bilateral lesions.
A parasol cell, sometimes called an M cell or M ganglion cell, is one type of retinal ganglion cell located in the ganglion cell layer of the retina. These cells project to magnocellular cells in the lateral geniculate nucleus of the thalamus as part of the magnocellular pathway in the visual system. They have large cell bodies, large branching dendrite networks, and fast conduction velocities. They are innervated by large receptive fields, but receive no information about color. Parasol ganglion cells contribute information about the motion and depth of objects to the visual system.
Chronostasis is a type of temporal illusion in which the first impression following the introduction of a new event or task-demand to the brain can appear to be extended in time. For example, chronostasis temporarily occurs when fixating on a target stimulus, immediately following a saccade. This elicits an overestimation in the temporal duration for which that target stimulus was perceived. This effect can extend apparent durations by up to 500 ms and is consistent with the idea that the visual system models events prior to perception.
Transsaccadic memory is the neural process that allows humans to perceive their surroundings as a seamless, unified image despite rapid changes in fixation points. The human eyes move rapidly and repeatedly, focusing on a single point for only a short period of time before moving to the next point. These rapid eye movements are called saccades. If a video camera were to perform such high speed changes in focal points, the image on screen would be a blurry, nauseating mess. Despite this rapidly changing input to the visual system, the normal experience is of a stable visual world; an example of perceptual constancy. Transsaccadic memory is a system that contributes to this stability.
The anti-saccade (AS) task is a gross estimation of injury or dysfunction of the frontal lobe, by assessing the brain’s ability to inhibit the reflexive saccade. Saccadic eye movement is primarily controlled by the frontal cortex.
Binocular switch suppression (BSS) is a technique to suppress usually salient images from an individual's awareness, a type of experimental manipulation used in visual perception and cognitive neuroscience. In BSS, two images of differing signal strengths are repetitively switched between the left and right eye at a constant rate of 1 Hertz. During this process of switching, the image of lower contrast and signal strength is perceptually suppressed for a period of time.
Peter H. Schiller is a professor emeritus of Neuroscience in the Department of Brain and Cognitive Sciences at the Massachusetts Institute of Technology (MIT). He is well known for his work on the behavioral, neurophysiological and pharmacological studies of the primate visual and oculomotor systems.