Audio drawing and working memory in blindness: design, development and validation of a multi-sensory system.

Working memory (WM) plays a crucial role in helping individuals perform everyday activities and interact with the external environment. However, despite valuable insights into visual memory mechanisms, the multi-sensory aspects of WM have not been thoroughly investigated, especially in congenitally blind individuals, primarily due to a lack of proper technologies. This work presents an audio-haptic system to study the generation and recall of multi-sensory spatial representations in visually impaired and sighted individuals. Precisely, we developed an audio-tactile tablet composed of a set of spatialized speakers covered by tactile sensors and tri-modal stimulations units providing acoustic, visual, and haptic feedback. Furthermore, we integrated these two systems among each other. Interestingly, visually impaired and sighted adults could easily interact with these devices. Technologies like the ones we developed might be suitable in experimental and clinical settings to study the influence of the different sensory modalities on high-level cognitive skills and the impact of early visual deprivation on such abilities for rehabilitative intervention since the first period of life.

An architectural hypothesis for direction selectivity in the visual cortex: the role of spatially asymmetric intracortical inhibition.

Within a linear field approach, an architectural model for simple cell direction selectivity in the visual cortex is proposed. The origin of direction selectivity is related to recurrent intracortical interactions with a spatially asymmetric character along the axis of stimulus motion. No explicit asymmetric temporal mechanisms are introduced or adopted. The analytical investigation of network behavior, carried out under the assumption of a linear superposition of geniculate and intracortical contributions, shows that motion sensitivity of the resulting receptive fields emerges as a dynamic property of the cortical network without any feed-forward direction selectivity bias. A detailed analysis of the effects of the architectural characteristics of the cortical network on directionality and velocity-response curves was conducted by systematically varying the model's parameters.

Analog VLSI circuits as physical structures for perception in early visual tasks.

A variety of computational tasks in early vision can be formulated through lattice networks. The cooperative action of these networks depends on the topology of interconnections, both feedforward and recurrent ones. This paper shows that it is possible to consider a distinct general architectural solution for all recurrent computations of any given order. The Gabor-like impulse response of a second-order network is analyzed in detail, pointing out how a near-optimal filtering behavior in space and frequency domains can be achieved through excitatory/inhibitory interactions without impairing the stability of the system. These architectures can be mapped, very efficiently at transistor level, on very large scale integration (VLSI) structures operating as analog perceptual engines. The problem of hardware implementation of early vision tasks can, indeed, be tackled by combining these perceptual agents through suitable weighted sums. A 17-node analog current-mode VLSI circuit has been implemented on a CMOS 2 microm, NWELL, single-poly, and double-metal technology, to demonstrate the feasibility of the approach. Applications of the perceptual engine to various machine vision algorithms are proposed.

Functional periodic intracortical couplings induced by structured lateral inhibition in a linear cortical network.

The spatial organization of cortical axon and dendritic fields could be an interesting structural paradigm to obtain a functional specificity without postulating highly specific feedforward connections. In this article, we investigate the functional implications of recurrent intracortical inhibition when it occurs through clustered medium-range interconnection schemes (Wörgötter & Koch, 1991; Somogyi, 1989; Kritzer, Cowey, & Somogyi, 1992). Moreover, the interaction between the inhibitory schemes and visual orientation maps is explored. Assuming linearity, we show that clustered inhibitory mechanisms can trigger a propagation process that allows the development of extra (i.e., induced) interactions among the cortical sites involved in the recurrent loops. In addition, we point out how these interactions functionally modify the response of cortical simple cells and yield to highly structured Gabor-like receptive fields. This study should be considered not as a realistic biological model of the primary visual cortex but as an attempt to explain possible computational principles related to intracortical connectivity and to the underlying single-cell properties.

Recurrent inhibition and clustered connectivity as a basis for Gabor-like receptive fields in the visual cortex.

A continuous-space model of visual cortex interactions which, starting from elongate Gaussian functions, leads to high-selective Gabor-like receptive fields, is proposed. The model is based on intracortical inhibition mechanisms occurring through medium-range clustered connections. The analysis, carried out under the assumption of a linear superposition of geniculate and intracortical contributions, shows how inhibition enhances both spatial and spatial-frequency selectivity. The effects of inhibition strength and of its spatial organization on the properties of the resulting receptive field are investigated. Specifically, the relationships between receptive fields and inhibition schemes are investigated by deriving analytical expressions for their dependence and through a systematic numerical parametric study. The emergence of periodic receptive fields, like the ones observed in neurophysiological measurements, is also pointed out in relation to the clustered nature of the inhibitory scheme.