Computational and Functional Hypotheses

Given the above observations, several possible functions and computational mechanisms for the long-range lateral connections have been proposed. The list below is by no means complete or even consistent, but it represents several of the views currently debated, including those put forward by the chapters in this book.

Modulating and controlling cortical responses

1. Recurrent lateral connections may permit amplification of weak stimuli and suppression of strong stimuli, thus providing a mechanism for activity normalization [40].

2. They may mediate competition and synchronization over large distances of cortex [41,42,45].

3. Lateral connection structures may be crucial for developing sharp orientation tuning and hyperacuity [11,36,40].

4. They may play a role in implementing attention and control [41].

Representing information

1. Lateral connections may store information for decorrelation of visual input, and filter out known statistical redundancies in the cortical representations [10,39].

2. They may store information for feature binding and grouping, such as Gestalt rules [11,35,38,44,45].

3. Lateral connections may form the substrate for encoding memories as attractors in the cortical network [41].

4. They may mediate the perceptual learning processes observed as early as the primary visual cortex by encoding local associations [10,11,42].

Development and plasticity

1. Lateral connections may develop by Hebbian self-organization. The patterns of lateral connections could be defined by activity correlations in the cortical network [39].

2. Connection development may be driven by a combination of intrinsic activity and visual experience [39].

3. Lateral interactions could play a crucial role in the development of cortical columns, such as those representing orientation, ocular dominance and spatial frequency [10,11,39].

4. Lateral connections may mediate reorganization of the cortex in response to drastic changes in the input environment (such as retinal lesions and input deprivation) [16,25,34,39].

Role in visual phenomena

1. Lateral connections may mediate perceptual filling-in, such as the filling-in of blind spots, perceptual completion and illusory contours [40,42].

2. Lateral interactions may be responsible for visual illusions, such as the tilt illusion and Poggendorf illusion, which involve interactions between neigboring feature detectors [42].

3. Lateral connections may help establish rotational and scaling invariance [11,47].

4. They may help establish direction selectivity and motion sensitivity [30].

5. Lateral connections between different ocular dominance areas may help binocular fusion, depth perception and stereo vision [27,28].

6. Lateral connections could mediate visual comparisons, such as those necessary for object recognition, figure-ground discrimination, and segmentation [11,31,40,45,47].