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Artificial vision and retinal prostheses
Published in A Peyman MD Gholam, A Meffert MD Stephen, D Conway MD FACS Mandi, Chiasson Trisha, Vitreoretinal Surgical Techniques, 2019
Humayun Mark S, Lakhanpal Rohit R, Weiland James D
However, some findings differed from previous studies. The results of the Rizzo and Wyatt group showed that stimulating a single electrode within the array often resulted in multiple phosphenes in blind subjects. Then, using geometric patterns of electrode stimulation, the investigators tested whether subjects could achieve simple pattern vision; definite form perception matching the stimulation pattern was not obtained in any of the blind or sighted subjects. In trials with multiple electrodes, three of the five blind RP patients accurately described phosphenes an average of only 32% of the time, as compared with 43% for the normal-sighted patient. The investigators stated that this relatively poor outcome may have been attributed to the limited two-point discrimination among the subjects, perhaps as a result of interference created by interelectrode electrical fields. One potentially encouraging result was that the patients’ percepts were reproducible 66% of the time, even if they did not always conform to the stimulus pattern. This could not be completely explained, and was attributed to an unknown methodical adjustment.44–;46
Rehabilitation of Visual Perceptual and Visual Spatial Disorders in Adults and Children
Published in Barbara A. Wilson, Jill Winegardner, Caroline M. van Heugten, Tamara Ownsworth, Neuropsychological Rehabilitation, 2017
Barbara A. Wilson, Joe Mole, Tom Manly
There are few accounts of recovery from visual object agnosia and some people are reported to have remained agnosic for many years (Kertesz, 1979; Sparr et al., 1991; Wilson, 1999). A few, however, learn, or are helped to learn, to compensate. Goodale and Milner (2004) say of their patient with object and face recognition problems: ‘she was able to use visuomotor tricks to compensate for the absence of form perception’ (p. 125).
Management of residual physical deficits
Published in Mark J. Ashley, David A. Hovda, Traumatic Brain Injury, 2017
Velda L. Bryan, David W. Harrington, Michael G. Elliott
An evaluation of the ability to perform purposeful movements on command or praxis is important for all people with TBI. Apraxia or dyspraxia may be obvious or subtle and may influence physical performances. Even in the person with mild TBI (MTBI), initiation and sequencing of functional motor acts need close observation for potential disorganization.75 Skills required to produce a design in two and three dimensions (e.g., assemble various items from written or illustrated instructions) relate to constructional praxis and block design. Form perception is assessed via the form board and examines the ability to differentiate variations in form.
The effect of mild traumatic brain injury on the visual processing of global form and motion
Published in Brain Injury, 2019
Mohammed M. Alnawmasi, Arijit Chakraborty, Kristine Dalton, Patrick Quaid, Benjamin T. Dunkley, Benjamin Thompson
Global form perception was tested psychophysically using a form detection task based on Glass patterns (Figure 1). The task was used to measure a form coherence threshold. Stimuli were generated by an Apple Macintosh computer using Psykinematix software and presented on 27-inch iMac display (1024 x 768 pixels resolution, 60 cm viewing distance). The stimuli were composed of bright pairs of dots presented on a grey background (100 cd/m2) and were presented for 1 second within a rectangular aperture (10º diameter). There were two populations of dot pairs: ‘‘signal pairs” which were arranged to form concentric- or cross-shaped radial Glass patterns constructed in a manner similar to that described by Wilson and Wilkinson (1998), and “noise pairs” which were oriented randomly within the display aperture (Figure 1). Form coherence was modulated by varying the ratio of signal to noise dots in the stimulus.
The effects of preterm birth on visual development
Published in Clinical and Experimental Optometry, 2018
Myra Ps Leung, Benjamin Thompson, Joanna Black, Shuan Dai, Jane M Alsweiler
The measurement of global form perception follows the same principles as global motion assessment, except that the stimuli are constructed from oriented elements such as stationary pairs of dots (dipoles), Gabor patches or short lines, each of which can be arranged to form shapes (see Figure 3 for stimulus examples).1969 The task requires the observer to detect a common orientation of elements or a shape embedded in randomly oriented elements.1969 By varying the signal to noise ratio in the stimulus, a coherence threshold can be measured (Figure 3). Other form perception tasks include finding a shape within a stimulus array of varying luminance, texture or contrast.1987 As with motion coherence thresholds, lower form coherence thresholds indicate a higher global form perception sensitivity (less signal is required to perform the task).
Fellow Eye Deficits in Amblyopia
Published in Journal of Binocular Vision and Ocular Motility, 2019
Eileen E. Birch, Krista R. Kelly, Deborah E. Giaschi
Additional support for the central role of binocular dysfunction in fellow eye deficits comes from our recent research on motion-defined form perception. Amblyopic children who have had evidence of abnormal binocularity, including nil stereo or only peripheral fusion, were significantly more likely to have a fellow eye deficit (Figure 7).