Eric A. Salzen

The Spatial Selectivity of Early and Late Waves within the Human Visual Evoked Response

Two studies on the amplitude, latency, and waveform of human visual evoked responses to the onset of sine-wave grating patterns were made. Results indicated that the peak latencies of both early and late waves were a function of the spatial frequency of the stimulus. The amplitude of the early wave (N1−P1) was consistently greatest at low spatial frequencies while the late wave (N2−P2) showed consistent attenuation at low spatial frequencies. In addition the location of the peak amplitude response of the late, but not the early, wave depended on the location (macular versus extramacular) and area (small versus large stimulus field) of retina stimulated. These findings are discussed in the light of evidence for separate transient and sustained systems within the human visual system.

A forebrain lesion preventing imprinting in domestic chicks

SummaryNewly hatched domestic chicks were subjected to bilateral aspiration lesions of the anterior, dorsal, posterior or lateral regions of the forebrain and then were reared separately with one of two types of imprinting object. Between 3 and 10 days later they were tested for imprinting, pecking accuracy, visual looming and auditory startle responses. Lateral and dorsal lesion groups differed from a control group in the number of successful discriminations of their imprinting object and the lateral group was not significantly different from a random expectancy. All groups were impaired in pecking accuracy but the lateral group was the most severely affected. Looming responses and post startle freezing behaviour were reduced only in the posterior and dorsal groups which were also the least responsive in the imprinting tests. It was concluded that the lateral forebrain area is critically and specifically involved in the visual learning of imprinting being necessary for the discrimination of, but not for approach responsiveness to, imprinting objects.

Forebrain lesions and retention of imprinting in domestic chicks

SummaryNewly-hatched domestic chicks were reared separately with one of two types of imprinting object hanging in their cages. On the 5th day discrimination tests demonstrated strong preferences for the familiar object. On the 6th day the chicks were subjected to bilateral aspiration lesions of either the anterior or the lateral forebrain and their imprinting objects removed from the cages. Discrimination tests were made on the 9th and 12th days, the imprinting objects replaced, and a final relearning test given on the 14th day. The anterior lesion group was slightly impaired in the retention and relearning tests while the lateral lesion group was drastically affected, being significantly worse than the anterior group and with choices only just significantly above random expectation in the retention tests and no different from random choice in the relearning test. It was concluded that a lateral forebrain region is necessary for retention and relearning of a previously acquired imprinted preference.

Event related potentials, reaction time, and cognitive performance in idiopathic Parkinson's disease

Sixteen non-demented patients with idiopathic Parkinsons disease (PD) with varying degrees of cognitive impairment and sixteen age-, sex- and education-matched normal controls were examined with (1) an auditory oddball paradigm requiring counting or a motor response in separate determinations, (2) a reaction time task with movement time component and (3) a detailed clinical and neuropsychological test battery. Patients were impaired on a number of neuropsychological tests. They also showed an increased P2 and N2 latency, but no significant increase in P3 latency. Their response initiation times and reaction times during the oddball experiment were not different from controls, whereas movement time was significantly increased. Increased peak latencies, particularly for N2, were moderately associated with Parkinsonian motor impairment in patients and with the Benton Multiple Choice Visual Retention Test in patients and controls. Movement time was associated with P3 latency only in controls and in both groups with the Benton Multiple Choice Visual Retention Test. The observed pattern of results suggests that in non-demented PD patients ERP peak latencies, visuo-spatial task performance and Parkinsonian motor impairment share a significant degree of variance. While impairments in neuropsychological tests and delay in the earlier peaks P2 and N2 do not appear to be sensitive to medication with L-DOPA, normal P3 latencies might indicate good pharmacological symptom control in the absence of dementia.

P300 and smooth eye pursuit: concordance of abnormalities and relation to clinical features in DSM-III schizophrenia.

Twenty‐five DSM‐III‐diagnosed schizophrenics and 37 normal and age‐matched controls were examined using an oddball paradigm for the generation of P300 and smooth eye‐pursuit tasks. Results were compared between groups and related to clinical characteristics, including a family history of psychiatric illness. Group differences were found for P300 amplitudes, latencies and eye‐tracking. A family history of psychiatric illness was associated with normal eye‐tracking in patients. Small P300 amplitudes alone and in combination with long P300 latencies were associated with a family history in controls.

The early wave of the visual evoked potential to sinusoidal gratings: Responses to quadrant stimulation as a function of spatial frequency

VEPs were elicited by sinusoidal grating patterns of differing spatial frequencies presented in each of the 4 quadrants of the visual field. Analysis of the early wave of the VEP indicated a pattern of polarity inversions when wave forms were compared across the horizontal meridian of the visual field. With the exception of low spatial frequencies, clear polarity inversions also occurred across the vertical meridian of the visual field in the case of laterally placed electrodes. Comparison of the clearly identifiable early peak with records for the same subject using central field stimulation showed the complexity of the latter records and the inherent difficulty of isolating and interpreting specific component waves of the VEP without adequate topographical data from quadrant stimulation.

The effects of forebrain lesions on innate and imprinted colour, brightness and shape preferences in domestic chicks.

In previous reports we have found that lesions of the lateral forebrain of domestic chicks prevent or destroy imprinted preferential discrimination of objects differing in colour/ brightness and shape. However, there were non-significant departures from random responding and it is possible that some residual learning was interacting with innate colour/ brightness preferences. An initial experiment in the present study showed that visually naive chicks had a significant blue and round shape preference when 1-2 days old. Visually experienced but non-imprinted chicks retained the round shape preference but showed weakened blue choice at 5-6 days of age. Chicks imprinted with a green slab showed a significant green preference at 5-6 days but chose slab and ball shapes equally. Taken together, these findings demonstrate imprinting for both colour and shape. Two further experiments tested lateral-, anterior-, and posterior-lesion and control chicks for retention of imprinted colour/brightness (mid-green) and shape (square) separately. Only the lateral- lesion group failed to choose the stimulus object with the familiar imprinted colour/brightness and instead chose the unfamiliar one (dark blue). No lesion group differed from the controls in the imprinted shape discriminations, all choosing the unfamiliar (round) as often as the familiar one. It appeared that the lateral-lesion chicks were like naive 1-day-olds in their colour/brightness preference but like imprinted birds in their shape preference. The final experiment tested the naive colour/brightness preferences of lateral- and anterior- lesion and control chicks using green and blue coloured discs in two tests with reversal of the brightness values. Both lesion groups behaved like controls in choosing dark blue in preference to light green. With reversed brightness values the controls showed a preference for the darker green discs, the anterior-lesion birds showed a slight tendency to choose the lighter blue disc, and the lateral-lesion birds reponded equally to the two colours. Thus, choices appeared to depend on brightness but in comparison with the controls there was some reduction in the brightness effect in the lateral-lesion birds and especially so in the anterior-lesion chicks. Since anterior lesions did not seriously impair the colour/brightness imprinted preference in the previous experiments, the reversal of the imprinted preference produced by lateral forebrain lesions is probably a true learning /memory loss and is not simply due to a colour or brightness sensory impairment.

Lower-bandpass filter frequency in P3 experiments: a possible cause for divergent results in schizophrenia research.

A review of the recent studies using auditory oddball paradigms in schizophrenia suggests that a low lower-bandpass frequency is associated with negative findings, whereas a high lower-bandpass frequency was used in those studies finding significant differences between schizophrenics and controls

The effect of different high-pass filter settings on peak latencies in the event-related potentials of schizophrenics, patients with Parkinson's disease and controls

Eighteen schizophrenic patients, 16 patients with idiopathic Parkinsons disease, and the same numbers of age, sex and education matched controls were examined with oddball experiments for the generation of P3. Individual averages were high-pass filtered at different cut-off frequencies with single-pole digital filters with equivalent analogue Butterworth filter profiles. The purpose of this procedure was to simulate analogue high-pass filters used in clinical studies from different centres and to examine their potential effect on group differences. Increasing high-pass filters resulted in a phase lead for all peaks examined (N1, P2, N2, P3). The only group differences were found for P3, which showed a greater phase lead in controls than in the patient groups, usually resulting in a more pronounced group difference. Similar wave forms and filter properties could be modelled by synthetic wave forms consisting of sine waves of different frequencies.

Facial Processing in the Dementias

A number of studies have investigated facial processing ability in different dementing conditions (e.g. Kurucz et al., 1979; Biber et al., 1981; Wilson et al., 1982). However, there has been no attempt to directly compare the performance of different diagnostic groups on the same facial processing tasks. This makes the delineation of communalities and differences in performance between different groups hard to assess. Such comparisons, were they to provide evidence of clear differences in facial processing ability between these groups, would also have the practical value of allowing facial processing tasks to be used as tools in differential diagnosis. This would be of particular value in differentiating between Dementia Alzheimer Type and Multi-Infarct Dementia as existing clinical and psychometric methods have their inadequacies (Liston and La Rue, 1983).