The cortical visual areas of the sheep.

Abstract

1. A stereotaxic method for the sheep brain is described. 2. At its widest part the primary visual area (Visual I) of each hemisphere extends approximately 20 mm anteroposteriorly and, when unfolded, approximately 35 mm from side to side. It occupies both walls of the lateral sulcus, and extends medially to the medial wall of the hemisphere and to the depth of the ectolateral sulcus laterally. 3. The most lateral part of the primary visual area includes 10‐15 degrees of the ipsilateral field; the contralateral field is represented to 135 degrees from the mid line. 4. Visual II also includes a strip of ipsilateral representation on its medial edge and extends to the supra‐sylvian sulcus on the lateral surface of the brain. The furthest lateral representation recorded was 130 degrees lateral. 5. Most of both visual areas is concerned with the area centralis and the visual streak. The remainder of the retina has very little cortical representation. 6. Most cells in Visual I are simple with orientational and sometimes directional sensitivity. Some complex and hypercomplex cells have been seen in Visual I, and these predominate in Visual II. Receptive field sizes from 0‐25 to 10 degree were found. Within 15 degrees of the vertical meridian, binocular cells are common in both Visual I and II.

Visuotopic organisation of striate cortex in the marmoset monkey (Callithrix jacchus)

“…However, we are not aware of any study of nasotemporal overlap in the marmoset. The representation of the ipsilateral field in V1 also exists in other mammals, where it tends to be larger than in primates (Clarke and Whitteridge, 1976;Volchan et al, 1988;Payne, 1990;Rosa et al, 1993). In the cat, Payne (1990) found evidence for both the callosal and the retinofugal pathways contributing to the ipsilateral representation in V1 and suggested that the two routes might operate synergistically.…”

Binocular visual mechanisms in cortical areas I and II of the sheep.

“…In both these areas, cells with fields within 15-20°of the mid line tended to be excited by both eyes, and to be selective not only to monocular stimulus properties such as position in the field and orientation (Clarke & Whitteridge, 1976), but also to specifically binocular properties. The latter are the main concern of this paper, but it should be remembered that the monocular requirements had to be met in addition to the binocular ones for a cell to respond optimally, and, in fact, the cells in V2 were more sharply tuned to orientation than were those in VI.…”

“…The methods were the same as in the preceding paper (Clarke & Whitteridge, 1976), with a few additions described here.…”

“…The responses of many units were recorded in both VI and V2 (as defined in the previous paper (Clarke & Whitteridge, 1976)). In both these areas, cells with fields within 15-20°of the mid line tended to be excited by both eyes, and to be selective not only to monocular stimulus properties such as position in the field and orientation (Clarke & Whitteridge, 1976), but also to specifically binocular properties.…”

Cortical representation of the horizon in V1 and peripheral scaling in mammals with lateral eyes.

“…When the visual streak is aligned to the horizon this retinal specialization allows the animal to view the whole horizon without the specialized eye movements required for scanning with an area or fovea centralis (Hughes, 1977). Indeed rabbits (Hughes, 1971), goats (Hughes & Whitteridge, 1973) and sheeps (Clarke & Whitteridge, 1976) also align the visual streak to the horizon to increase resolution and motion detection. In these species even a casual observation at their heads suggests that the visual field of these animals area unusually large (Hughes, 1977;Picanço Diniz, 1987).…”