Little is known about the development of the sensitivity for “optic flow,” a large-scale pattern perceived during locomotion. The present study aimed to examine infants' coherence thresholds to radial optic flow motion during the first months of life. Using a forced-choice preferential looking technique, infants' sensitivities were measured with a moving radial stimulus varying in coherence on one side and a corresponding non-directional radial noise pattern on the other. Coherence thresholds for 11 infants from each of 2, 4, 6, 8, and 10 months of age groups were studied by a constant stimuli method. In the second experiment, seven infants were followed longitudinally (tested at 2, 4, 6, and 8 months) using the same stimuli. Results of both studies demonstrated significant improvement for the sensitivity of expanding radial motion during the first months of life. Finally, the 2 directions of radial motion were tested (expanding and contracting) for participants followed longitudinally (from 2 to 8 months). Data showed superior sensitivity for expansion versus contraction direction of motion. This dissociation may suggest that sensitivity to direction corresponding with forward locomotion (expansion) develops at a faster rate than the opposite direction encountered when moving backwards (contraction). The sensitivity improvement for expanding patterns likely reflects the maturation of cerebral areas subtending motion integration in infancy.

During locomotion, an observer sees a large and complex pattern of visual motion called optic flow. This phenomenon is characterized by elements in the environment accelerating and expanding as they move peripherally. In cats, previous studies have indicated that the posteromedial part of the lateral suprasylvian (PMLS) cortex may be involved in the processing of optic flow fields. We further addressed this issue by studying the importance of specific parameters of the optic flow patterns and investigating whether cell responses to these stimuli depend on receptive field (RF) location in the visual field. Results can be summarized as follows: approximately two-thirds of PMLS cells responded to optic flow fields and a subset of these (84/153) showed a clear direction selectivity for motion along the frontal axis. Of these units, the majority responded preferentially to expansion rather than contraction of the pattern. Cells' responses depend on RF location in the visual field. For centrally located RFs, tested both when the origin of motion was within the RF or at the area centralis, responses were generally comparable whether or not size or speed gradients were removed from the optic flow pattern. A different tendency was observed for peripherally located RFs. In general, these cells exhibited a preferred direction almost exclusively when the origin of motion was placed at the area centralis, and neuronal discharges and direction selectivity for many of them were reduced when the optic flow cues were removed from the pattern. The results of this study suggest that there may be functional differences in response properties between PMLS cells located in the central and peripheral parts of the visual field that may reflect a specialization of the PMLS cortex in optic flow processing.

The pulvinar is the largest extrageniculate visual nucleus in mammals. Given its extensive reciprocal connectivity with the visual cortex, it allows the cortico-thalamocortical transfer of visual information. Nonetheless, knowledge of the nature of the pulvinar inputs to the cortex remains elusive. We investigated the impact of silencing the pulvinar on the contrast response function of neurons in 2 distinct hierarchical cortical areas in the cat (areas 17 and 21a). Pulvinar inactivation altered the response gain in both areas, but with larger changes observed in area 21a. A theoretical model was proposed, simulating the pulvinar contribution to cortical contrast responses by modifying the excitation-inhibition balanced state of neurons across the cortical hierarchy. Our experimental and theoretical data showed that the pulvinar exerts a greater modulatory influence on neuronal activity in area 21a than in the primary visual cortex, indicating that the pulvinar impact on cortical visual neurons varies along the cortical hierarchy.