Brain injuries can cause insidious gaps in the visual "fields" - insidious because, more often than not, a person with visual field losses is unaware of the problem. Just as people with hearing losses sometimes feel that others are mumbling, people with visual field losses may actually feel that the world has changed, e.g., why are they making clocks that way?
People without brain injuries, who think they are seeing everything, may be shocked to learn that they too have gaps in their vision. Known as "physiological blind spots" these gaps are caused by the lack of sensory receptors where the nerve leaves the eye to carry visual information to the brain. You have one in each eye, about the size of a fist at arm's length. Close one eye and try to locate yours. Is it on the inside or the outside? In each eye it is located a little to the outside and slightly down from where you are looking.
People with gaps in the visual fields caused by brain injury, therefore, may have a double disability: the loss of vision and the loss of awareness. Normally, the nervous system tends to fill in the background and to lose the figure. So if such a person were to attempt to drive (not recommended!), they might see the road, but not a pedestrian or child running into the street.
Brain injury can cause different patterns of loss, including blind spots and tunnel vision. However, most common is a pattern called "homonymous hemianopia" in which corresponding halves of the fields are lost in each eye. For instance, in left homonymous hemianopia the blindness affects the left side of each eye. The blindness may be absolute (complete) or relative (reduced sensitivity).
It is not easy to test for visual field losses, especially if there are cognitive problems caused by the brain injury. And since people are often unaware of the loss, it is quite possible that the losses will remain undiagnosed. Fortunately, our computerized methods have been developed to check for visual field impairment. Because these techniques offer immediate feedback, they can be used to build awareness and to lay a foundation for treatment.
This program detects slowed response to visual stimuli in all quadrants of the computer display. Respond with switch/joystick or mouse button. Accurate (machine-speed independent) response times mapped in patient comprehensible display. This procedure can be used to detect slowed response to visual stimuli-either on the right or left side or both sides, as well as the top, middle, and bottom. With eyes free to move, the procedure is a 'functional' visual field, more like everyday life than conventional visual field measurement which involves fixation. Immediate response time feedback is reinforced by the final results, which include a map of slowed responding in various parts of the visual field. This feedback, unlike any traditional visual field measurement procedure, offers the patient information which may improve their awareness (and ultimately insight) of their sensory loss.
Stimuli are flashed on the left, right or both sides. Although fixation isn't required, the brevity of the display makes compensation difficult. Relative difficulty on simultaneous trials suggests "extinction" or "hemi-neglect." SDSST is one of the "PERFIELD" tasks for evaluating "functional peripheral visual fields." It represents an intermediate point in the spectrum of informational density / attentional demand: from REACT (the simplest) to SEARCH (the most complex). Bender used the classic confrontation procedure to test for the "extinction" phenomenon. This computerized procedure tests for extinction in the visual modality. The idea is to test for responsivity in both visual fields, presenting stimuli singly and, on other trials, two simultaneously. Extinction is said to occur when the individual responds to all single stimuli, but on double simultaneous trials fails to report one of the stimuli, usually the one which was on the affected side. Extinction is important because it suggests an attentional component to the hemi-field impairment, as opposed to a purely sensory loss.
An 8 by 8 array of homogeneous shapes ("Martians") is
searched for one different shape (a "sleeping" Martian). Search times are
recorded from when the display appears to when the ultimately successful response was
initiated.
This program is designed to detect differences in attention and responsiveness on the two
sides of the visual field. It is particularly designed to identify those persons who have
a spatial hemi-imperception which affects their ability to scan both sides of a display
efficiently and, used in conjunction with SEARCH, it differentiates this skill from shape
examination and matching. The display contains an intermediate level of information
compared to REACT (one stimulus in an otherwise empty display) and SEARCH (an 8 x 8 array
of heterogeneous shapes). This variation in information density enables one to
differentiate hemi-inattention and hemi-imperception. The patient searches an array of
identical patterns (which can be interpreted as the heads of little space people) for the
"odd" one (the one which appears to have closed its eyes). Using this analogy
and the instruction "Find the one that fell asleep", SOSH becomes simple to
understand. From trial to trial, the display stays the same; only the location of the
target shape changes. Locations throughout the array are sampled and search times are
reported and recorded for each. Median search times are computed for left side and right
side targets, respectively.
Based on a classic visual search task by Poppelreuter, this task requires the location of a target shape in an 8 x 8 array of different shapes. The shapes are abstract geometric patterns. Search time is recorded and analyzed by location. SEARCH for Shapes is informationally dense and designed to demand much attention to all areas of the display. It is a task which calls for many skills, ranging from visual inspection, short-term visual memory, uniform scanning on both sides of the display, to sustained attention and frustration tolerance. SEARCH for Shapes involves visual search for the match to a centrally placed abstract pattern in an array of other shapes. None of the shapes is easily named and some are similar to the target. Response time is automatically recorded and displayed together with a distinctive double beep when quicker than a predesignated criterion value.