A passive wearable microfluidic sensor for the 24 hour monitoring of intraocular pressure using a smartphone.
A stimulus (mask) reduces the visibility of another stimulus (target) when they are presented in close spatio-temporal vicinity of each other, a phenomenon called visual masking. Visual masking has been extensively studied to understand dynamics of information processing in the visual system. In this study, we adopted a statistical point of view, rather than a mechanistic one, to investigate how mask-related activities might influence target-related ones within the context of visual masking. We modeled the distribution of response errors of human observers in three different visual masking experiments, namely para-/meta-contrast masking, pattern masking by noise, and pattern masking by structure. We adopted statistical models, which have been used previously in studies of visual short-term memory, to capture response characteristics of observers under masking conditions. We tested the following scenarios: (i) mask activity may reduce a target's signal-to-noise ratio (SNR) without interfering with its encoding precision. (ii) Mask activity may "interfere" with the encoding of a target and cause decreased precision in observer's reports. (iii) Decreased performance due to masking may result from the confusion or "misbinding" of a mask's features with those of the target, when they are similar as in the case of pattern masking by structure. Our results show that in all three types of masking, the reduction of a target's SNR was the primary process whereby masking occurred. A significant decrease, correlated with masking strength, in the precision of the target's encoding was observed in para-/meta-contrast and pattern masking by structure, but not in pattern masking by noise. We interpret these findings as the mask reducing the target's SNR (i) by suppressing or interrupting the signal of the target in para-/meta-contrast, (ii) by increasing noise in pattern masking by noise, and (iii) a combination of the two in pattern masking by structure.
The all-fluidic low-pass filtering feature of dilatometric strain sensors has the potential to suppress physiological noise.
Our results show that motion information available only to the deviated eye can drive optokinetic eye movements. We conclude that the brain has access to visual information from portions of the deviated eye (including the fovea) in strabismus that it can use to drive eye movements.
Visual masking and attention have been known to control the transfer of information from sensory memory to visual short-term memory. A natural question is whether these processes operate independently or interact. Recent evidence suggests that studies that reported interactions between masking and attention suffered from ceiling and/or floor effects. The objective of the present study was to investigate whether metacontrast masking and attention interact by using an experimental design in which saturation effects are avoided. We asked observers to report the orientation of a target bar randomly selected from a display containing either two or six bars. The mask was a ring that surrounded the target bar. Attentional load was controlled by set-size and masking strength by the stimulus onset asynchrony between the target bar and the mask ring. We investigated interactions between masking and attention by analyzing two different aspects of performance: (i) the mean absolute response errors and (ii) the distribution of signed response errors. Our results show that attention affects observers' performance without interacting with masking. Statistical modeling of response errors suggests that attention and metacontrast masking exert their effects by independently modulating the probability of Bguessing^b ehavior. Implications of our findings for models of attention are discussed.
The preferred treatment for correcting strabismus in humans involves the surgical manipulation of extraocular muscles (EOM). Although widely practiced, this treatment has varying levels of success and permanence, possibly due to adaptive responses within the brain or at the muscle. We investigated neural plasticity following strabismus surgery by recording responses from cells in the oculomotor and abducens nuclei before and after two monkeys with exotropia (divergent strabismus) underwent a strabismus correction surgery that involved weakening of the lateral rectus (LR) and strengthening of the medial rectus (MR) muscle of one eye. Eye movement and neuronal data were collected for a period of 6-10 months after surgery during a monocular viewing smooth-pursuit task. These data were fit with a first-order equation and resulting coefficients were used to estimate the population neuronal drive (ND) to each EOM of the viewing and deviated eyes. Surgery resulted in an ~70% reduction in strabismus angle in both animals that reverted towards pre-surgical misalignment by about 6 months after treatment. In the first month after surgery, the ND to the treated MR reduced in one animal and ND to the LR increased in the other animal, both indicating active neural plasticity that reduced the effectiveness of the treatment. Although these neuronal drive changes resolved by 6 months, we also found evidence for an inappropriate peripheral muscle adaptation that limited the effectiveness of surgery over the long term. Outcome of strabismus correction surgery could be improved by identifying ways to enhance ‘positive’ adaptation and limit ‘negative’ adaptation.Significance statementThis is the first study of its kind to longitudinally follow behavioral and neural responses before and after a typical strabismus correction surgery in a monkey model for strabismus. We show the nature of muscle and neuronal plasticity that follows strabismus correction surgery.
PurposeAlthough widely practiced, surgical treatment of strabismus has varying levels of success and permanence. In this study we investigated adaptive responses within the brain and the extraocular muscles (EOM) that occur following surgery and therefore determine long-term success of the treatment.MethodsSingle cell responses were collected from cells in the oculomotor and abducens nuclei before and after two monkeys (M1, M2) with exotropia (divergent strabismus) underwent a strabismus correction surgery that involved weakening of the lateral rectus (LR) and strengthening of the medial rectus (MR) muscle of one eye. Eye movement and neuronal data were collected for up to 10 months after surgery during a monocular viewing smooth-pursuit task. These data were fit with a first-order equation and resulting coefficients were used to estimate the population neuronal drive (ND) to each EOM of both eyes.ResultsSurgery resulted in a ∼70% reduction in strabismus angle in both animals that reverted toward presurgical misalignment by approximately 6 months after treatment. In the first month after surgery, the ND to the treated MR reduced in one animal and ND to the LR increased in the other animal, both indicating active neural plasticity that reduced the effectiveness of the treatment. Adaptive changes in ND to the untreated eye were also identified.ConclusionsActive neural and muscle plasticity corresponding to both the treated and the untreated eye determines longitudinal success following surgical correction of strabismus. Outcome of surgical treatment could be improved by identifying ways to enhance “positive” adaptation and limit “negative” adaptation.
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