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Humans blink their eyes frequently during normal viewing, more often than it seems necessary for keeping the cornea well lubricated. Since the closure of the eyelid disrupts the image on the retina, eye blinks are commonly assumed to be detrimental to visual processing. However, blinks also provide luminance transients rich in spatial information to neural pathways highly sensitive to temporal changes. Here, we report that the luminance modulations from blinks enhance visual sensitivity. By coupling high-resolution eye tracking in human observers with modeling of blink transients and spectral analysis of visual input signals, we show that blinking increases the power of retinal stimulation and that this effect significantly enhances visibility despite the time lost in exposure to the external scene. We further show that, as predicted from the spectral content of input signals, this enhancement is selective for stimuli at low spatial frequencies and occurs irrespective of whether the luminance transients are actively generated or passively experienced. These findings indicate that, like eye movements, blinking acts as a computational component of a visual processing strategy that uses motor behavior to reformat spatial information into the temporal domain. [ABSTRACT FROM AUTHOR]

Establishing a representation of space is a major goal of sensory systems. Spatial information, however, is not always explicit in the incoming sensory signals. In most modalities it needs to be actively extracted from cues embedded in the temporal flow of receptor activation. Vision, on the other hand, starts with a sophisticated optical imaging system that explicitly preserves spatial information on the retina. This may lead to the assumption that vision is predominantly a spatial process: all that is needed is to transmit the retinal image to the cortex, like uploading a digital photograph, to establish a spatial map of the world. However, this deceptively simple analogy is inconsistent with theoretical models and experiments that study visual processing in the context of normal motor behavior. We argue here that, as with other senses, vision relies heavily on temporal strategies and temporal neural codes to extract and represent spatial information. [ABSTRACT FROM AUTHOR]

Following a period of quiescence at the end of last century, the study of microsaccades has now regained strong impetus and broad attention within the vision research community. This wave of interest, partly fueled by the advent of user-friendly high-resolution eyetrackers, has attracted researchers and led to novel ideas. Old hypothesis have been revisited and new ones formulated. This article is designed to serve as a practical guide for researchers in the field. Because of the history of the field and the difficulty of measuring very small eye movements, the study of microsaccades presents peculiar challenges. Here, we summarize some of the main challenges and describe methods for assessing and improving the quality of the recordings. Furthermore, we examine how these experimental challenges have influenced analysis of the visual functions of microsaccades and critically review current evidence on three long-debated proposals: the maintenance of fixation, the prevention of visual fading, and the exploration of fine spatial detail. [ABSTRACT FROM AUTHOR]

In a moving agent, the different apparent motion of objects located at various distances provides an important source of depth information. While motion parallax is evident for large translations of the agent, a small parallax also occurs in most head/eye systems during rotations of the cameras. A similar parallax is also present in the human eye, so that a redirection of gaze shifts the projection of an object on the retina by an amount that depends not only on the amplitude of the rotation, but also on the distance of the object with respect to the observer. This study examines the accuracy of distance estimation on the basis of the parallax produced by camera rotations. Sequences of human eye movements were used to control the motion of a pan/tilt system specifically designed to reproduce the oculomotor parallax present in the human eye. We show that the oculomotor strategies by which humans scan visual scenes produce parallaxes that provide accurate estimation of distance. This information simplifies challenging visual tasks such as image segmentation and figure/ground segregation. [Copyright &y& Elsevier]

Under natural viewing conditions, small movements of the eye, head and body prevent the maintenance of a steady direction of gaze. It is known that stimuli tend to fade when they are stabilized on the retina for several seconds. However, it is unclear whether the physiological motion of the retinal image serves a visual purpose during the brief periods of natural visual fixation. This study examines the impact of fixational instability on the statistics of the visual input to the retina and on the structure of neural activity in the early visual system. We show that fixational instability introduces a component in the retinal input signals that, in the presence of natural images, lacks spatial correlations. This component strongly influences neural activity in a model of the LGN. It decorrelates cell responses even if the contrast sensitivity functions of simulated cells are not perfectly tuned to counter-balance the power-law spectrum of natural images. A decorrelation of neural activity at the early stages of the visual system has been proposed to be beneficial for discarding statistical redundancies in the input signals. The results of this study suggest that fixational instability might contribute to the establishment of efficient representations of natural stimuli. [ABSTRACT FROM AUTHOR]

Like all saccades, microsaccades cause both spatial and temporal changes in the input to the retina. In space, recent studies have shown that these small shifts precisely relocate a narrow (smaller than the foveola) high-acuity retinal locus on the stimulus. However, it has long been questioned whether the temporal modulations resulting from microsaccades are also beneficial for vision. To address this question, we combined spectral analysis of the visual input to the retina with measurements of contrast sensitivity in humans. Estimation of how different types of eye movements redistribute the power of an otherwise stationary stimulus shows that small saccades contribute more temporal power than ocular drift in the low-frequency range, suggesting a specific role for these movements in the encoding of low spatial frequencies. However, an influence on contrast sensitivity was only found for saccades with amplitudes larger than 30'. Contrast thresholds remained highly similar in the presence and absence of smaller saccades. Furthermore, saccades of all amplitudes, including microsaccades, were strongly suppressed during exposure to the stimulus. These findings do not support an important function of the visual transients caused by microsaccades. [ABSTRACT FROM AUTHOR]

Summary Much evidence indicates that humans and other species process large-scale visual information before fine spatial detail. Neurophysiological data obtained with paralyzed eyes suggest that this coarse-to-fine sequence results from spatiotemporal filtering by neurons in the early visual pathway. However, the eyes are normally never stationary: rapid gaze shifts (saccades) incessantly alternate with slow fixational movements. To investigate the consequences of this oculomotor cycle on the dynamics of perception, we combined spectral analysis of visual input signals, neural modeling, and gaze-contingent control of retinal stimulation in humans. We show that the saccade/fixation cycle reformats the flow impinging on the retina in a way that initiates coarse-to-fine processing at each fixation. This finding reveals that the visual system uses oculomotor-induced temporal modulations to sequentially encode different spatial components and suggests that, rather than initiating coarse-to-fine processing, spatiotemporal coupling in the early visual pathway builds on the information dynamics of the oculomotor cycle. [ABSTRACT FROM AUTHOR]

Humans use rapid gaze shifts, known as saccades, to explore visual scenes. These movements yield abrupt luminance changes on the retina, which elicit robust neural discharges at fixation onsets. Yet little is known about the spatial content of saccade transients. Here, we show that saccades redistribute spatial information within the temporal range of retinal sensitivity following two distinct regimes: saccade modulations counterbalance (whiten) the spectral density of natural scenes at low spatial frequencies and follow the external power distribution at higher frequencies. This redistribution is a consequence of saccade dynamics, particularly the speed/amplitude/duration relation known as the main sequence. It resembles the redistribution resulting from inter-saccadic eye drifts, revealing a continuum in the modulations given by different eye movements, with oculomotor transitions primarily acting by regulating the bandwidth of whitening. Our findings suggest important computational roles for saccade transients in the establishment of spatial representations and lead to testable predictions about their consequences for visual functions and encoding mechanisms. • By formatting the input flow, saccades play an important computational role in vision • At low spatial frequencies, saccades discard redundant information in natural scenes • The bandwidth of this effect (whitening) increases as saccade amplitude decreases • The whitening bandwidth oscillates during the natural saccade/fixation cycle Humans use saccades (rapid gaze shifts) to explore visual scenes. Mostofi et al. show that these eye movements flexibly reformat the luminance flow on the retina in a way that selectively discards redundant information present in natural scenes. These results reveal a matching between saccade dynamics and the characteristics of the natural world. [ABSTRACT FROM AUTHOR]