Acuity for spatial periodicity in human vision

340 ity, after diazepam treatment, reflects the presence of slowly dissociating endogenous ligand for BZR in the synaptic junction resulting, in its turn, in the enhancement of BZ-GABA-Cl receptor complex and providing the development of membrane hyperpolarization. Thus, based on the neurochemical investigations on the adequate models of pathology of nervous system we may suggest a view on some molecular mechanisms of the development of neurosis-like state, adaptability to the stressful situations and the action of some psychotropic drugs.

mus, on the one hand, and by its facilitation of the inhibitory effect of corticoids on the CRF secretion, on the other. Alpha-adrenoreceptor blockers and mianserine did not effect the DST indices in suppressors, where as they decreased basic and specially postdexamethasone cortisol levels and, respectively, increased the degree of suppression. The obtained data suggest that in endogenic depression, there is a positive feedback between the serotonin and norepinephrine deficit in the brain cortisol hypersecretion while normally these precesses are controlled by the negative feedback. A detailed description of the DST technique applied is presented in Nuller and Ostroumova (1978).

DISORDERS OF NEUROENDOCRINE REGULATION IN ENDOGENIC DEPRESSION

References

Yu. L. Nuller Department of Biological Therapy, the Bekhterev Psychoneurological Research Institute, Leningrad, USSR One hundred and forty six depressives were subjected to the dexamethasone suppression test (DST) prior to and during therapy with mianserine, desimipramine, nonselective alpha-adrenoreceptor blockers like phentolamine and pirroxan, with L-tryptophane, bephol, an antidepressant with prevailing serotoniergic actiort L-DOPA, salbutalol, a beta-adrenoreceptor agonist, and propranolol, a beta-adrenoreceptor antagonist. The DST technique consisted in the following: - blood samples were taken at 9 p.m. for two days running for cortisol assessment, at 11 p.m. of the first day the patients were given 0.5 mg dexamethasone. The main index was not the post-dexamethasone content but the percentage of cortisol suppression by dexamethasone. This index reflects intactness of the central mechanisms of regulation in cortisol secretion to a greater degree. Suppression of less than 40% was considered pathological (positive DST). The obtained results were analyzed separately for suppressors and non-suppressors. L-tryptophan and bephol were not found to effect the basic cortisol level and drastically increased the degree of suppression. With the account taken of the data reported in the literature as regards the serotonin effect on the isolated hypothalamus and the experiments on animals, the obtained findings can be explained by the serotonin’s direct stimulation of the CRF secretion by hypothala-

Nuller Yu. L., Ostroumova M.N. (1978). Disorder of Homeostatic Regulation in Adrenal Functioning in Patients With Endogenic Depression. (In Russian). J. Neuropathol. Psychiat. USSR, 78:381. Nuller Yu. L. , Ostroumova M.N. (1980) Resistance to Inhibiting Effect of Dexamethasone in Patients With Endogenous Depression. Acta Psychiat. &and., 61: 167-177.

ACUITY FOR SPATIAL PERIODICITY IN HUMAN VISION G. Nyman and J. Karlsson Department of Psychology, University of Helsinki Ritarikatu 5, 00170 Helsinki, Finland The phase spectrum of a signal carries much of the critical information about the signal (cf. Oppenheim and Lim, 1981). For human vision, the role of phase spectrum in image coding is less clear. It is known, for example, that in fovea1 vision, the spatial phase discrimination ability can be of the order of hyperacuity when rapid phase changes (Westheimer, 1978), movement, or both (Morgan and Watt, 1982) are induced to the stimuli. The use of temporal transients in producing the spatial phase shifts leaves open the question whether phase discrimination ability without the contribution from temporally selective mechanisms would be equally good. If the visual system were to represent part of the image information by a global phase code, then it

341 would be expected to be sensitive to major phase changes in the image field. On the other hand, the use of local processing for image coding would require high sensitivity only to local phase changes. We have studied the ability of human observers to discriminate simultaneous phase relationships between two vertical sinusoidal gratings that were separated by a narrow stripe whose luminance was equal to the mean luminance of the sinusoids. By varying the stripe width it was possible to study the spatial extent of the simultaneous, or parallel phase processing in spatial vision. Method The subject fixated at the middle of the stripe that

separated the two parts of the grating. A 2AFC paradigm was used in which the subject had to tell whether the randomly presented stimuli were two sinusoids in phase or two sinusoids out of phase. If the response to the stimulus block was correct then the phase difference was decreased by 0.08 rad, otherwise it was increased by the same amount. Results

When the phase discrimination threshold obtained by the 2AFC method was plotted as a function of the gap width and expressed in min of arc, the data fell on a strain line. The data was fitted by a least squares line. The relative phase sensitivity (the inverse of the phase discrimination threshold) was measured separately for a 0.5 c/deg grating. Now the discrimination performance deteriorated quickly when the size of the gap was increased. The data was fitted with a function that describes the output of a double gaussian (DOG)filter that is assumed to be located in the middle of the stripe so that its response is affected optimally by both sides of the grating. The DOG-falter had the familiar form: R(x) = exP(-(x-&)2/s2)-0.57exp(-(x-x$/(1.75s)2 The standard deviation of the DOG-function was chosen so that its peak response was at the spatial frequency of 1.47f,, where f,= 0.5 c/deg, i.e. the fundamental frequency studied. Thin gave a reasonable fit to the data of the two observers participating in the experiments and suggested that higher spatial Erequen-

ties than the fundamental might underlie the observed poor phase discrimination performance. By using a noise band as a masking stimulus it was possible to determine which spatial frequency band was actually used in the parallel phase discrimination task. The data of one subject show where the peak masking is seen to occur at the frequencies higher than the fundamental of the grating. Discussion The surprisingly poor performance in discriminating

the phase relationships over an area having the width of only about 1 cycle of the fundamental frequency, suggests that the visual system is capable of accurate phase discrimination only within a very localized part of the visual field. In the case of sinusoidal gratings the metric for determining the dimensions of this local area could be based on the period length of the fundamental frequency component. Furthermore, the masking experiments suggest that phase discrimination was based on the activity of relatively high frequency channels which had the estimated bw at half height of about 1.5 octaves. The lack of effective parallel phase processing even over narrow distances excludes the possibility that chase discrimination would be performed as an interval discrimination task nor by ‘coincidence detectors’ suggested by Morgan and Regan (1987).

INDICES OF IMPAIRED CENTRAL INFORMATION PROCESSING IN PATIENTS SUFFERING FROM CHRONIC RENAL DISEASE I. Ochsenfart, N. Roth, R. Kielstein, L. Lachhein Institute of Physiology, Clinic of Internal Medicine, Medical Academy Magdeburg, G.D.R. Introduction

Chronical renal failure is a problem of functional restriction of kidneys with permanent retention of urea1 substance. The most frequent causes are glomerulonephritis, pyelonephritis, congenital malformations, and diabetic nephropathy. The following classification of renal failure has been clinically proved: 1. phase of full compensation: 2. phase of compensational retention: 3. phase of decompensational retention: and 4. end-stage renal disease.