The present paper describes the results of architectural and electrophysiological mapping observations of the medial bank of the suprasylvian sulcus of the ferret immediately caudal to somatosensory regions. The aim was to determine if the ferret possessed a homologous cortical area to the anteromedial lateral suprasylvian visual area (AMLS) of the domestic cat. We studied the architectural features and visuotopic organization of a region that we now consider to be a homologue to the cat AMLS. This area showed a distinct architecture and retinotopic organization. The retinotopic map was complex in nature with a bias towards representation of the lower visual field. These features indicate that the region described here as AMLS in the ferret is indeed a direct homologue of the previously described cat AMLS and forms part of a hierarchy of cortical areas processing motion in the ferret visual cortex. With the results of the present study and those of earlier studies a total of twelve cortical visual areas have been determined presently for the ferret, all of which appear to have direct homologues with visual cortical areas in the cat (which has a total of eighteen areas).

The receptive-field positions and orientation preferences of neurons occupying the same tangential location in visual cortex are thought to be similar but to have an associated random scatter. However, previous estimates of this scatter may have been inflated by the use of subjective plotting methods, sequential recording of single units, and residual eye movements. Here we report measurements of receptive-field position and orientation scatter in cat area 17 made with tetrodes, which were able to simultaneously isolate and record up to 11 nearby neurons (ensembles). We studied 355 units at 72 sites with moving light and dark bars. Receptive-field sizes and positions were estimated by least-squares fitting of Gaussians to response profiles. We found that receptive-field position scatter was about half of the ensemble average receptive-field size. We confirmed previous estimates of orientation scatter, but calculations suggested that much of it may be accounted for by anatomical scatter in the positions of recorded neurons relative to the tetrode in a smooth map. Orientation tuning width was positively correlated with the degree of orientation scatter. Scatter was not independent in the two eyes: deviations from the local mean for both preferred orientation and receptive-field position were correlated although a significant amount of residual inter-ocular orientation and receptive-field position scatter was present. We conclude that cortical maps of orientation and receptive-field position are more ordered than was previously thought, and that random scatter in receptive-field positions makes a relatively small contribution to cortical point image size.