Microsaccades Counteract Visual Fading during Fixation

SummaryOur eyes move continually, even while we fixate our gaze on an object. If fixational eye movements are counteracted, our perception of stationary objects fades completely, due to neural adaptation. Some studies have suggested that fixational microsaccades refresh retinal images, thereby preventing adaptation and fading. However, other studies disagree, and so the role of microsaccades remains unclear. Here, we correlate visibility during fixation to the occurrence of microsaccades. We asked subjects to indicate when Troxler fading of a peripheral target occurs, while simultaneously recording their eye movements with high precision. We found that before a fading period, the probability, rate, and magnitude of microsaccades decreased. Before transitions toward visibility, the probability, rate, and magnitude of microsaccades increased. These results reveal a direct link between suppression of microsaccades and fading and suggest a causal relationship between microsaccade production and target visibility during fixation

Microsaccades: a neurophysiological analysis

Microsaccades are the largest and fastest of the fixational eye movements, which are involuntary eye movements produced during attempted visual fixation. In recent years, the interaction between microsaccades, perception and cognition has become one of the most rapidly growing areas of study in visual neuroscience. The neurophysiological consequences of microsaccades have been the focus of less attention, however, as have the oculomotor mechanisms that generate and control microsaccades. Here we review the latest neurophysiological findings concerning microsaccades and discuss their relationships to perception and cognition. We also point out the current gaps in our understanding of the neurobiology of microsaccades and identify the most promising lines of enquiry

Area V1 responses to illusory corner-folds in Vasarely's nested squares and the Alternating Brightness Star illusions.

Vasarely's nested squares illusion shows that the corners of concentric squares, arranged in a gradient of increasing or decreasing luminance, generate illusory "corner-folds," which appear more salient (either brighter or darker) than the adjacent flat (non- corner) regions of each individual square. The Alternating Brightness Star (ABS) illusion, based on Vasarely's classic nested squares, further shows that the strength of these corner-folds depends on corner angle. Previous psychophysical studies showed the relationship between corner angle and perceived contrast in the ABS illusion to be linear, with sharp angles looking higher in contrast, and shallow angles lower in contrast. Center-surround difference-of-Gaussians (DOG) modeling did not replicate this linear relationship, however, suggesting that a full neural explanation of the nested squares and ABS illusions might be found in the visual cortex, rather than at subcortical stages. Here we recorded the responses from single area V1 neurons in the awake primate, during the presentation of visual stimuli containing illusory corner-folds of various angles. Our results showed stronger neural responses for illusory corner-folds made from sharper than from shallower corners, consistent with predictions from the previous psychophysical work. The relationship between corner angle and strength of the neuronal responses, albeit parametric, was apparently non-linear. This finding was in line with the previous DOG data, but not with the psychophysical data. Our combined results suggest that, whereas corner-fold illusions likely originate from center-surround retinogeniculate processes, their complete neural explanation may be found in extrastriate visual cortical areas

Building a US company to manufacture solar PV mounting systems

This paper describes the process of developing a product for the solar industry. It is the story of starting a business in the solar market by designing a product, manufacturing the product and growing sales to over $1 million USD in 2011 and 2012. The author is describing the actual details of a manufacturing company that produces solar racking systems in the USA. The author founded the company in 2009 and left the company at the end of 2012. The document describes the changing landscape of the racking sector of the US PV market, and makes the case for industry standards in solar module dimensions. The range of current sizes of solar modules is described. The inconsistency in sizes creates additional overhead for manufacturers to accommodate different sized parts to hold the different solar panels. A uniform standard size would result in cost reductions for the end customers

Fixational Eye Movement Correction of Blink-Induced Gaze Position Errors

<div><p>Our eyes move continuously. Even when we attempt to fix our gaze, we produce “fixational” eye movements including microsaccades, drift and tremor. The potential role of microsaccades versus drifts in the control of eye position has been debated for decades and remains in question today. Here we set out to determine the corrective functions of microsaccades and drifts on gaze-position errors due to blinks in non-human primates (Macaca mulatta) and humans. Our results show that blinks contribute to the instability of gaze during fixation, and that microsaccades, but not drifts, correct fixation errors introduced by blinks. These findings provide new insights about eye position control during fixation, and indicate a more general role of microsaccades in fixation correction than thought previously.</p></div

Microsaccades decrease large and increase small blink-induced fixation errors.

<p>(<b>A</b>) Vertical eye-position traces after 11 randomly-selected blinks that led to large vertical errors ([0.64–0.66 deg], monkey Y). (<b>B</b>) Vertical eye-position traces after 11 randomly-selected blinks that led to small vertical errors ([0.14–0.16 deg], monkey Y). (<b>A, B</b>) Grey band: range of final eye positions resulting in a positive CR. Brown traces: microsaccades decreased the blink-induced error. Orange traces: microsaccades increased the error. [We note that, although we considered all blinks in our analyses, blinks that took the eye below the fixation point were relatively infrequent (∼18%). Thus, this figure illustrates the more typical situation where blinks induced errors above the fixation point].</p

Blink-induced error and microsaccade properties.

<p>(<b>A</b>) Normalized magnitude distributions of blink-induced fixation errors, post-blink microsaccades, and post-blink drifts across non-human primates. The distribution of post-blink microsaccade magnitudes matches closely that of blink-induced fixation errors. (<b>B</b>) Polar histogram of the directions of blink-induced fixation errors, post-blink microsaccades, and post-blink drifts. Blink-induced fixation errors are more likely directed upward. Post-blink microsaccades tend to move the eye downward, thus counteracting the error introduced by the blink. (<b>C</b>) Latency distribution for post-blink microsaccades (all monkeys combined): 74.12% of post-blink microsaccade onsets occurred in the initial 400 msec after the end of the blink. (<b>D</b>) Blink-induced error as a function of time, from the end of the blink onward. We calculated the blink-induced error at every point in time, whether there were concurrent microsaccades or drifts. The blink-induced error declines gradually, showing the largest decrease in the initial 400 msec interval, simultaneous to the highest production of post-blink microsaccades. Shaded area indicates the SEM across monkeys (<i>n</i> = 5 monkeys).</p

Average magnitude of fixation errors induced by different types of ocular events.

<p>Fixation errors associated with blinks tended to be larger than those associated with (all) microsaccades or drifts, but not significantly so.</p><p>Average magnitude of fixation errors induced by different types of ocular events.</p