Morash V.S.,Smith Kettlewell Eye Research Institute
IEEE World Haptics Conference, WHC 2015 | Year: 2015
Movement strategies were investigated in a one-handed haptic search task where blindfolded sighted participants used either one or five fingers to find a landmark on an unstructured tactile map. Search theory predicts that systematic strategies, such as parallel sweeps and spirals, should be more prevalent when the searcher's detection radius is small (one finger) than when the detection radius is large (five fingers). Movement patterns were classified as either non-systematic or systematic. As predicted by search theory, systematic strategies were more common in one-finger than five-finger searches. Overall, these results indicate that systematic haptic search strategies are used and modulated by detection radius for untrained sighted participants. © 2015 IEEE.
Song J.-H.,Smith Kettlewell Eye Research Institute |
McPeek R.M.,New York University
Journal of Neurophysiology | Year: 2010
Most visual scenes are complex and crowded, with several different objects competing for attention and action. Thus a complete understanding of the production of goal-directed actions must incorporate the higher-level process of target selection. To examine the neural substrates of target selection for visually guided reaching, we recorded the activity of isolated neurons in the dorsal premotor area (PMd) of monkeys performing a reaction-time visual search task. In this task, monkeys reached to an odd-colored target presented with three distractors. We found that PMd neurons typically discriminate the target before movement onset, ∼150-200 ms after the appearance of the search array. In one subset of neurons, discrimination occurred at a consistent time after search array onset regardless of when the reaching movement occurred, suggesting that these neurons are involved in target selection. In a second group of neurons, discrimination time depended on reach reaction time, consistent with involvement in movement production but not in target selection. To look for physiological corroboration of these two functionally defined groups, we analyzed the extracellular spike waveforms of recorded neurons. This analysis showed a population of neurons with narrow action potentials that carried signals related to target selection. A second population with broader action potentials was more heterogeneous, with some neurons showing activity related to target selection and others showing only movement production activity. These results suggest that PMd contains signals related to target selection and movement execution and that different signals are carried by distinct neural subpopulations. Copyright © 2010 The American Physiological Society.
Xiao B.,Smith Kettlewell Eye Research Institute
Journal of vision | Year: 2010
Cortical responses to spatially discrete patches of achromatic luminance contrast can be altered by the presence of high-contrast, spatially remote "surrounds" and this achromatic "surround suppression" has been the subject of much recent research. However, the nature of long-range contrast normalization in chromatic signals has been less studied. Here we use a combination of neuroimaging data from source-imaged EEG and two different psychophysical measures of surround suppression to study contrast normalization in stimuli containing achromatic luminance and S-cone-isolating contrast. In an appearance matching task, we find strong within-channel but little between-channel suppression. However, using a contrast increment detection task, we do find evidence for weak but significant between-channel effects. Our neural measurements agree with the appearance matching data, showing significant within-channel suppression and no significant interactions between signals initiated in different pre-cortical pathways. We hypothesize that appearance judgments and V1 population responses are dominated by neurons with chromatically matched classical and extra-classical surrounds while contrast increment detection tasks rely on a subpopulation of neurons that have extra-classical surrounds sensitive to both chromatic and achromatic contrasts. Our psychophysical and source-imaged EEG results are consistent with a hypothesis based on natural scene statistics that long-range contrast normalization in early visual system is largely driven by signals within the same chromatic channel.
McKee S.P.,Smith Kettlewell Eye Research Institute |
Taylor D.G.,Smith Kettlewell Eye Research Institute
Journal of Vision | Year: 2010
We measured binocular and monocular depth thresholds for objects presented in a real environment. Observers judged the depth separating a pair of metal rods presented either in relative isolation, or surrounded by other objects, including a textured surface. In the isolated setting, binocular thresholds were greatly superior to the monocular thresholds by as much as a factor of 18. The presence of adjacent objects and textures improved the monocular thresholds somewhat, but the superiority of binocular viewing remained substantial (roughly a factor of 10). To determine whether motion parallax would improve monocular sensitivity for the textured setting, we asked observers to move their heads laterally, so that the viewing eye was displaced by 8-10 cm; this motion produced little improvement in the monocular thresholds. We also compared disparity thresholds measured with the real rods to thresholds measured with virtual images in a standard mirror stereoscope. Surprisingly, for the two naive observers, the stereoscope thresholds were far worse than the thresholds for the real rodsVa finding that indicates that stereoscope measurements for unpracticed observers should be treated with caution. With practice, the stereoscope thresholds for one observer improved to almost the precision of the thresholds for the real rods. © ARVO.
Cottereau B.R.,Stanford University |
McKee S.P.,Smith Kettlewell Eye Research Institute |
Norcia A.M.,Stanford University
Journal of Neurophysiology | Year: 2012
The human stereoscopic system is remarkable in its ability to utilize widely separated features as references to support fine depth discrimination. In a search for possible neural substrates of this ability, we recorded high-density EEG and used a distributed inverse technique to estimate population-level disparity responses in five regions of interest (ROIs): V1, V3A, hMT+, V4, and lateral occipital complex (LOC). The stimulus was a central modulating disk surrounded by a correlated "reference" annulus presented in the fixation plane. We varied a gap separating the disk from the annulus parametrically from 0 to 5.5° as a test of long-range disparity integration. In the V1, LOC, and hMT+ ROIs, the responses with gaps >0.5° were equal to those obtained in a control condition where the surround was composed of uncorrelated noise (no reference). By contrast, in the V4 and V3A ROIs, responses with gaps as large as 5.5° were still significantly higher than the control. As a test of the spatial distribution of the disparity reference information, we manipulated the properties of the stimulus by placing noise between the center and the surround or throughout the surround. The V3A ROI was particularly sensitive to disparity noise between the center and annulus regions, suggesting an important contribution of disparity edge detectors in this ROI. © 2012 the American Physiological Society.
Colenbrander A.,Smith Kettlewell Eye Research Institute
Acta Ophthalmologica | Year: 2010
This article, based on a report prepared for the International Council of Ophthalmology (ICO) and the International Society for Low Vision Research and Rehabilitation (ISLRR), explores the assessment of various aspects of visual functioning as needed to document the outcomes of vision rehabilitation. Documenting patient abilities and functional vision (how the person functions) is distinct from the measurement of visual functions (how the eye functions) and also from the assessment of quality of life. All three areas are important, but their assessment should not be mixed. Observation of task performance offers the most objective measure of functional vision, but it is time-consuming and not feasible for many tasks. Where possible, timing and error rates provide an easy score. Patient response questionnaires provide an alternative. They may save time and can cover a wider area, but the responses are subjective and proper scoring presents problems. Simple Likert scoring still predominates but Rasch analysis, needed to provide better result scales, is gaining ground. Selection of questions is another problem. If the range of difficulties does not match the range of patient abilities, and if the difficulties are not distributed evenly, the results are not optimal. This may be an argument to use different outcome questions for different conditions. Generic questionnaires are appropriate for the assessment of generic quality of life, but not for specific rehabilitation outcomes. Different questionnaires are also needed for screening, intake and outcomes. Intake questions must be relevant to actual needs to allow prioritization of rehabilitation goals; the activity inventory presents a prototype. Outcome questions should be targeted at predefined rehabilitation goals. The Appendix cites some promising examples. The Low Vision Intervention Trial (LOVIT) is an example of a properly designed randomized control study, and has demonstrated the remarkable effectiveness of vision rehabilitation. It is hoped that further similar studies will follow. © 2009 Acta Ophthalmol.
Verghese P.,Smith Kettlewell Eye Research Institute
Vision Research | Year: 2012
This study examines saccade strategy in a novel task where observers actively search a display to find multiple targets in a limited time. Theory predicts that the relative merit of different saccade strategies depends on the prior probability of the target at a location: when the target prior is low and multiple-target trials are rare, making a saccade to the most likely target location is close to the optimal strategy, but when the target prior is high and multiple-target trials are frequent, selecting uncertain locations is more informative. The prior probability of the target was varied from 0.17 to 0.67 to determine whether observers adjusted their saccades strategies to maximize information. Observers actively searched a noisy display with six potential target locations. Each location had an independent probability of a target, so the number of targets in a trial ranged from 0 to 6. For all target priors ranging from low to high, a trial-by-trial analysis of saccade strategy indicated that observers made saccades to the most likely target location more often than the most uncertain location. Fixating likely locations is efficient only when multiple targets are rare, as in the case of a low target prior, or in the case of the more standard single-target search task. Yet it is the preferred saccade strategy in all our conditions, even when multiple targets are frequent. These findings indicate that humans are far from ideal searchers in multiple-target search. © 2012 Elsevier Ltd.
Quinn G.E.,Children's Hospital of Philadelphia |
Good W.V.,Smith Kettlewell Eye Research Institute
Archives of Ophthalmology | Year: 2011
Objective: To compare grating (resolution) visual acuity at 6 years of age in eyes that received early treatment (ET) for high-risk prethreshold retinopathy of prematurity (ROP) with that in eyes that underwent conventional management (CM). Methods: In a randomized clinical trial, infants with bilateral, high-risk prethreshold ROP (n=317) had one eye undergo ET and the other eye undergo CM, with treatment only if ROP progressed to threshold severity. For asymmetric cases (n=84), the high-risk prethreshold eye was randomized to ET or CM. Main Outcome Measure: Grating visual acuity measured at 6 years of age by masked testers using Teller acuity cards. Results: Monocular grating acuity results were obtained from 317 of 370 surviving children (85.6%). Analysis of grating acuity results for all study participants with high-risk prethreshold ROP showed no statistically significant overall benefit of ET (18.1% vs 22.8% unfavorable outcomes; P=.08).Whenthe 6-year grating acuity results were analyzed according to a clinical algorithm (high-risk types 1 and 2 prethreshold ROP), a benefit was seen in type 1 eyes (16.4% vs 25.2%; P=.004) undergoing ET, but not in type 2 eyes (21.3% vs 15.9%; P=.29). Conclusion: Early treatment of eyes with type 1 ROP improves grating acuity outcomes, but ET for eyes with type 2 ROP does not. Application to Clinical Medicine: Type 1 eyes should be treated early; however, based on acuity results at 6 years of age, type 2 eyes should be cautiously monitored for progression to type 1 ROP. Trial Registration: clinicaltrials.gov Identifier: NCT00027222 ©2011 American Medical Association. All rights reserved.
Katzner S.,University College London |
Katzner S.,Smith Kettlewell Eye Research Institute |
Katzner S.,University of Tübingen |
Busse L.,University College London |
And 2 more authors.
Journal of Neuroscience | Year: 2011
GABAA inhibition is thought to play multiple roles in sensory cortex, such as controlling responsiveness and sensitivity, sharpening selectivity, and mediating competitive interactions. To test these proposals, we recorded in cat primary visual cortex (V1) after local iontophoresis of gabazine, the selective GABAA antagonist. Gabazine increased responsiveness by as much as 300%. It slightly decreased selectivity for stimulus orientation and direction, often by raising responses to all orientations. Strikingly, gabazine affected neither contrast sensitivity nor cross-orientation suppression, the competition seen when stimuli of different orientation are superimposed. These results were captured by a simple model in which GABAA inhibition has the same selectivity as excitation and keeps responses to unwanted stimuli below threshold. We conclude that GABAA inhibition in V1 helps enhance stimulus selectivity but is not responsible for competition among superimposed stimuli. It controls the sensitivity of V1 neurons by adjusting their response gain, without affecting their input gain © 2011 the authors.
Manduchi R.,University of California at Santa Cruz |
Coughlan J.M.,Smith Kettlewell Eye Research Institute
Conference on Human Factors in Computing Systems - Proceedings | Year: 2014
Smartphone apps can use object recognition software to provide information to blind or low vision users about objects in the visual environment. A crucial challenge for these users is aiming the camera properly to take a well-framed picture of the desired target object. We investigate the effects of two fundamental constraints of object recognition- frame rate and camera field of view- on a blind person's ability to use an object recognition smartphone app. The app was used by 18 blind participants to find visual targets beyond arm's reach and approach them to within 30 cm. While we expected that a faster frame rate or wider camera field of view should always improve search performance, our experimental results show that in many cases increasing the field of view does not help, and may even hurt, performance. These results have important implications for the design of object recognition systems for blind users. Copyright © 2014 ACM.