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Biomedical subjects

B G Hertz

Publications and source records attributed to B G Hertz.

15 recordsLinked to original sources
PubMed1992

Effect of mental retardation and motor disability on testing with visual acuity cards.

The visual acuity of 77 children (aged between 1 1/2 and eight years) with cerebral palsy and mental retardation was tested using acuity cards. Results varied by no more than one octave in 79 per cent of the cases. The median acuity of children with severe motor disabilities was lower and the variability from test to test was greater than for those with mild motor disabilities. Grouping the children roughly according to degree of mental retardation, the more retarded group tended to be more visually disabled and vary more from test to test. In general, day-to-day variability was greater than within-day inter-observer variability. The use of acuity cards to evaluate visual acuity in severely disabled and mentally retarded children, whose acuity is difficult to evaluate with conventional acuity tests, is a useful alternative method.

Adolescent↗
PubMed1988

Acuity card testing of patients with cerebral visual impairment.

Acuity card tests of 11 patients with cerebral visual impairment, unexplained by clinical and electrophysiological ophthalmic examinations, confirmed the suspicion of severe visual impairment in all but one patient, but resulted in acuity estimates higher than previous evaluations for all nine of the patients for whom an estimate could be made. Relatively good inter-test agreement supports the use of acuity cards for the quantitative evaluation of the vision of these patients.

Adolescent↗
PubMed1987

Acuity card testing of retarded children.

Evaluating the vision of retarded children is important, but it is often very difficult because the children cannot cooperate with the usual symbol recognition acuity tests. A total of 33 unselected children with Down's syndrome were tested with a standard symbol recognition test (Osterberg) and with a new test using acuity cards, which contain black and white square-wave gratings. The acuity cards were found to be useful for testing this group, both in terms of the children's ability to cooperate with the test and the test-retest variability of the results. Although eyes with strabismic amblyopia showed better acuity for gratings than for symbols, there was general agreement with symbol recognition acuities of the same patients. Acuity cards were also used to test 19 severely retarded young children with cerebral palsy, who were unable to be tested with symbols. Acuity card tests were almost always possible with this group, too, though test-retest variability was greater for these children. Acuity card testing can provide useful information about the visual acuity of many retarded children in less than 10 minutes.

Adolescent↗
PubMed1981

Effects of different hypothetical detection mechanisms on the shape of spatial-frequency filters inferred from masking experiments: I. Noise masks.

The detectability of a sinusoidal grating was measured in a standard two-interval forced-choice experiment against backgrounds of noise gratings of the same orientation as the signal. The noise gratings were either spatially high-pass or low-pass filtered and were either unchanged in each observation interval (static) or flickering at a rate that depended on their cutoff frequency (dynamic). Spatial-frequency-selective mechanisms are inferred from the data and their characteristics shown to depend on assumptions concerning the detection process thought to follow the spatial-frequency-selective device.

Humans↗
PubMed1977

Convergence of rod and cone signals in the cat's retina.

1. In an attempt to understand the convergence of rod and cone signals in the cat's retina, ganglion cells that received inputs from both rods and cones were stimulated using lights chosen to excite one or other receptor system or both together.2. If a mesopic background was chosen to allow the ganglion cell to be excited by a blue-green test flash primarily through rods and a deep red flash primarily through cones, one light could not be alternated with the other without eliciting a response from the cell.3. This appears to be a result of the different temporal properties of the scotopic and photopic systems. On the mesopic background responses to blue-green test flashes were transient. Responses to red test flashes arose with similar latency, but were more sustained.4. Rod and cone systems responded with similar latencies in the presence of the mesopic background that substantially light-adapted the rod system but left the full sensitivity of the cone system undiminished. When equivalently light-adapted, the cone system was faster.5. When brief flashes that acted through rods were presented with flashes that acted through cones the ganglion cell's response was the sum of the responses to the two flashes presented separately, as long as the flashes were weak. This linear relation ceased to hold when flashes were strong, but the breakdown appears not to be the result of mutual inhibition between rod and cone signals.6. When a background light excited both rod and cone systems it appeared to reduce sensitivity independently in each.7. The scotopic and photopic receptive fields of a given ganglion cell always were of the same type, on- or off-centre, and, within the limits of measurement, the central regions of the receptive fields were concentric and both the same size.

Action Potentials↗
PubMedDate not supplied

Use of the acuity card method to test retarded children in special schools.

Acuity cards were used to measure the visual acuity of students at a special school for retarded children, including some who were profoundly retarded and spastic. Almost all children could be tested by two testers on each of two days, and the agreement between different tests was good for children with acuities better than 0.2. Children with poorer acuities had poorer agreement between different test results. High success rate in testing and generally good inter-test agreement indicate that acuity cards can be used in a special school setting to obtain information about the vision of retarded children, who are much more likely than other children to suffer from poor vision.

Adolescent↗
PubMedDate not supplied

Acuity card testing of spastic children: preliminary results.

Acuity card testing of spastic children showed a high success rate. Agreement between repeated tests for children with mild motor handicaps was within the limits reported for non-handicapped children. Although more of the children with severe motor handicaps had greater test-retest variabilities, the majority of results from this group also showed an acceptable agreement. The high success rate and good test-retest agreement indicate that acuity cards can be very useful for testing children with cerebral palsy, who often have reduced acuity.

Cerebral Palsy↗