Temporal properties of human cones: an electroretinographic study

Abstracts 7th IOP Scientific Meeting /Internntional to shorter wavelengths with increasing depth. Surface species have cones with h,,, at about 546,525 and 450 nm and rods at 523 nm, deeper living species retain cones, but with h,,, shifting towards 500 and 425 nm and with rods at 480 nm, whereas the deepest living fish possess only rods (h,,, 480-500 nm). The amino acid sequences of the rod opsins derived from the nucleotide sequences of the opsin genes isolated from genomic DNA, show significant amino acid between-species substitutions that can be correlated with the different h maxof the visual pigments and are most likely responsible for the spectral tuning of the pigments. The nucleotide sequence data also provide a means of establishing the phylogenetic relationships of these closely related endemic species.

Reference Bowmaker, J.K., Govardovskii, V.I., Shukolyukov, S.A., Zeueva, L.V., Hunt, D.M., Sideleva, V.G. and Smimova. O.G. (1994) Visual pigments and the photic environment: the cottoid fish of Lake Baikal. Vision Res., 34: 591-605.

Temporal properties of human troretinographic study

cones:

J.K. Bowmaker, A.V. Whitmore, hstitrrte mology, University of London, Lordon, UK

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Retinal photoreceptors are the transducers and input filters of the visual system, responsible for converting photon fluxes into electrical activity in the nervous systems. While the spectral characteristics of these filters are now well characterised in humans and other primates, their temporal properties have received relatively less attention. Are there differences in the response kinetics of the different cone classes in humans and what effect (if any) does light adaptation have on these temporal characteristics? The answers to these questions are of fundamental importance since the ultimate limit on the temporal resolution of the visual system must be set by the response properties of the retinal cones: no amount of post-receptoral processing can put back information that has been lost at the input stage. We have shown that it is possible to use the cornea1 electroretinogram and a rapidly modulated sinusoidal stimulus (33 Hz) to isolate the massed electrical responses of the human long-wave-sensitive (LWS) and middle-wave-sensitive (MWS) cones in a normal human trichromat. Using a modified silent substitution technique and a combination of hardware and off-line digital signal processing we have examined the temporal properties of the LWS and MWS cones under various conditions of light adaptation in a normal human observer. The visual stimulus, forming a uniformly illuminated 11” field, consisted of a mixture of two monochromatic lights the wavelengths (560 nm and 660

Journal of Psychophysiology 18 (1994) 87-159

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nm) of which were chosen to stimulate primarily the MWS and LWS cones. The relative intensity of these two lights was adjusted so that they would result in equal quanta1 catches in one class of cone. A sinusoidal alternation was then set up (at 33 Hz) between the two lights such that the exchange was silent for one class of cone. The massed response from the remaining class (either MWS or LWS) was then isolated by monitoring the fundamental Fourier component of the electroretinogram. We report that the MWS cones exhibit a shorter phase delay relative to a 33-Hz sinusoidal stimulus than do the LWS cones with the LWS class lagging some 130” behind the MWS class. This is consistent with previous suction electrode and psychophysical observations on humans and other primates. We further show that for the range of adapting intensities tested, there are no changes in the temporal properties of either class with light adaptation. This finding is also consistent with the results of suction electrode experiments on the macaque retina and differs from the situation found in many lower vertebrates.

EEG reactivity in children with learning disabilities and in matched normal controls E. Braeker, C. Hug, A. Federspiel, M. Koukkou, EEG-Brain-Mapping Laboratory, University Hospital of Psych&r): CH-3072 BernJOstermundipen, Switzerland

It has been shown that information-induced EEG changes (EEG reactivity; EEG components of an adaptive orienting response) are closely related to the quality of learning and memory. EEG reactivities that are characterised by a decrease in the mean power and an increase in the mean frequency go in parallel with more successful learning processes. We have tested for differences and/or similarities of the characteristics of EEG reactivity to auditory information in children both with and without learning disabilities (LD). Nine children with learning disabilities out of special LD classes and 9 sex- and age-matched children out of regular classes of the public school system (8 boys, 1 girl; mean age 12.11+0.4 years) participated in the study. The 19channel EEG recordings (average reference) were collected during initial resting and before and after the presentation of four short nonsense sentences (mean duration 2.9 set) and four tones. The subjects were asked to keep the sentences in mind for later recall and to prompt the tones by pressing a button. The 40 set of resting EEG (20 x 2 set artefact-free epochs) and 20 set of EEG after the stimulus presentation (10 x 2 set artefact-free epochs) were spectrally analysed. Each spectral distribution was divided into frequency bands. The integrated mean power of each band was computed and used to calculate the EEG reactivity as the arithmetic difference between EEG epochs