Towards a Unified Theory of Neocortex: Laminar Cortical Circuits for Vision and Cognition

A key goal of computational neuroscience is to link brain mechanisms to behavioral functions. The present article describes recent progress towards explaining how laminar neocortical circuits give rise to biological intelligence. These circuits embody two new and revolutionary computational paradigms: Complementary Computing and Laminar Computing. Circuit properties include a novel synthesis of feedforward and feedback processing, of digital and analog processing, and of pre-attentive and attentive processing. This synthesis clarifies the appeal of Bayesian approaches but has a far greater predictive range that naturally extends to self-organizing processes. Examples from vision and cognition are summarized. A LAMINART architecture unifies properties of visual development, learning, perceptual grouping, attention, and 3D vision. A key modeling theme is that the mechanisms which enable development and learning to occur in a stable way imply properties of adult behavior. It is noted how higher-order attentional constraints can influence multiple cortical regions, and how spatial and object attention work together to learn view-invariant object categories. In particular, a form-fitting spatial attentional shroud can allow an emerging view-invariant object category to remain active while multiple view categories are associated with it during sequences of saccadic eye movements. Finally, the chapter summarizes recent work on the LIST PARSE model of cognitive information processing by the laminar circuits of prefrontal cortex. LIST PARSE models the short-term storage of event sequences in working memory, their unitization through learning into sequence, or list, chunks, and their read-out in planned sequential performance that is under volitional control. LIST PARSE provides a laminar embodiment of Item and Order working memories, also called Competitive Queuing models, that have been supported by both psychophysical and neurobiological data. These examples show how variations of a common laminar cortical design can embody properties of visual and cognitive intelligence that seem, at least on the surface, to be mechanistically unrelated.National Science Foundation (SBE-0354378); Office of Naval Research (N00014-01-1-0624

Perceptual organization and consciousness

With chapter written by leading researchers in the field, this is the state-of-the-art reference work on this topic, and will be so for many years to come

Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Boundary contour based surface representation.

We receive most information about our surrounding space and objects through the eyes. To reconstruct the 3D space and objects in the visual system from the 2D retinal images, surface representation must be a critical intermediate stage in the visual processing stream. It is hypothesized in the dissertation that the visual system represents textured surface by a border-to-interior strategy: boundary contours would be encoded first and then border-ownership assignments would be resolved. This process would solve the related problems such as figure-ground segregation, surface depth relationship, occlusion, transparency, etc. As a result, the boundary contours of the surfaces would be well defined and then the visual system could register the local features in different domains with the boundary contours, gradually from the adjacent areas of the boundary contours to the interior of the surfaces. To testify this hypothesis in the current proposal, a monocular boundary contour (MBC) paradigm is adapted from earlier studies by Ooi and He (2005, 2006). In Chapter 1, the boundary-contour-based hypothesis, with the MBC paradigm, is used to re-address a decade-long debate about binocular vision: whether (and how) binocular integration and inhibition coexist. In Chapter 2–5, the MBC-induced binocular suppression is systematically investigated, especially in Chapter 3 where the cortical speed of the hypothesized border-to-interior spreading is quantitatively estimated. In the end, the rules how the surface fragments are integrated to a global representation is further studied in Chapter 6 and 7, especially focusing on the role of luminance and color contrast polarities

Primary visual cortex activity along the apparent-motion trace reflects illusory perception

The illusion of apparent motion can be induced when visual stimuli are successively presented at different locations. It has been shown in previous studies that motion-sensitive regions in extrastriate cortex are relevant for the processing of apparent motion, but it is unclear whether primary visual cortex (V1) is also involved in the representation of the illusory motion path. We investigated, in human subjects, apparent-motion-related activity in patches of V1 representing locations along the path of illusory stimulus motion using functional magnetic resonance imaging. Here we show that apparent motion caused a blood-oxygenation-level-dependent response along the V1 representations of the apparent-motion path, including regions that were not directly activated by the apparent-motion-inducing stimuli. This response was unaltered when participants had to perform an attention-demanding task that diverted their attention away from the stimulus. With a bistable motion quartet, we confirmed that the activity was related to the conscious perception of movement. Our data suggest that V1 is part of the network that represents the illusory path of apparent motion. The activation in V1 can be explained either by lateral interactions within V1 or by feedback mechanisms from higher visual areas, especially the motion-sensitive human MT/V5 complex

Induction of Kanizsa Contours Requires Awareness of the Inducing Context

It remains unknown to what extent the human visual system interprets information about complex scenes without conscious analysis. Here we used visual masking techniques to assess whether illusory contours (Kanizsa shapes) are perceived when the inducing context creating this illusion does not reach awareness. In the first experiment we tested perception directly by having participants discriminate the orientation of an illusory contour. In the second experiment, we exploited the fact that the presence of an illusory contour enhances performance on a spatial localization task. Moreover, in the latter experiment we also used a different masking method to rule out the effect of stimulus duration. Our results suggest that participants do not perceive illusory contours when they are unaware of the inducing context. This is consistent with theories of a multistage, recurrent process of perceptual integration. Our findings thus challenge some reports, including those from neurophysiological experiments in anaesthetized animals. Furthermore, we discuss the importance to test the presence of the phenomenal percept directly with appropriate methods

Temporal Characteristics of Monoptic, Dichoptic and Half-Binocular Collinear Lateral Masking of Contrast Detection

Purpose: The temporal characteristics of dichoptic contrast integration across space in primary visual cortex are relatively unknown. This study investigated the effect of varying interstimulus interval (ISI) and flank duration on contrast detection threshold (CDT) of a sinusoid target under monoptic, dichoptic and half-binocular viewing. Methods: Eleven subjects with normal vision participated for a mean of 25 hours each. In the main experiment, target and flanks were 3 cpd vertical sinusoids with 6 lambda (sigma = 1.5 lambda) center-to-center vertical separation. Flank contrast was normalized to 3X flank CDT. Flanks were presented at 4 durations (67-500ms) and ISIs were presented at 8 durations (0-2500ms) resulting in 0-3000ms stimulus onset asynchronies (SOA). Target presentations were 250ms to dominant eye using a mirror haploscope and septum. Flanks were presented to dominant (monoptic and half-binocular) and non-dominant eyes (dichoptic and half-binocular). Forward masking was used throughout with a 1-FC detection paradigm and 7-level MOCS. Each target CDT was the product of approximately 700 trials. Results: As expected, simultaneous presentation resulted in CDT facilitation (monoptic = 19%± 3.86% (SE), dichoptic = 13.9%± 4.00%, half-binocular = 18.0%± 4.20%). For all viewing conditions, relative facilitation decreased as SOA increased up to 1000ms. Unexpectedly, dichoptic flanks produced significant CDT suppression (p \u3c 0.05) at 500-1000ms SOAs that was maximal at the 1000ms SOA (9.9%± 5.1%). All viewing conditions approached no effect at the longest SOAs (1500-3000ms). Flank duration had a significantly greater contribution to the overall effect than ISI for monoptic (p \u3c 0.01) and half-binocular (p \u3c 0.05) viewing. Discussion: The collinear CDT facilitation produced by intra-ocular and inter-ocular flanks at shorter SOAs is consistent with lateral connections in primary visual cortex. The temporal aspects of longer SOA, dichoptic CDT suppression observed in this study are consistent with prior studies of illusory contour perception. Conclusion: I propose the novel hypothesis that the CDT suppression produced by dichoptic collinear flanks at longer SOAs is due to one-way, contrast adaptation from lateral propagation that produced the effect of a collinear, illusory contour. This hypothesis was supported by the results of a supplemental, orthogonal flank experiment

Spiking Dynamics during Perceptual Grouping in the Laminar Circuits of Visual Cortex

Grouping of collinear boundary contours is a fundamental process during visual perception. Illusory contour completion vividly illustrates how stable perceptual boundaries interpolate between pairs of contour inducers, but do not extrapolate from a single inducer. Neural models have simulated how perceptual grouping occurs in laminar visual cortical circuits. These models predicted the existence of grouping cells that obey a bipole property whereby grouping can occur inwardly between pairs or greater numbers of similarly oriented and co-axial inducers, but not outwardly from individual inducers. These models have not, however, incorporated spiking dynamics. Perceptual grouping is a challenge for spiking cells because its properties of collinear facilitation and analog sensitivity to inducer configurations occur despite irregularities in spike timing across all the interacting cells. Other models have demonstrated spiking dynamics in laminar neocortical circuits, but not how perceptual grouping occurs. The current model begins to unify these two modeling streams by implementing a laminar cortical network of spiking cells whose intracellular temporal dynamics interact with recurrent intercellular spiking interactions to quantitatively simulate data from neurophysiological experiments about perceptual grouping, the structure of non-classical visual receptive fields, and gamma oscillations.CELEST, an NSF Science of Learning Center (SBE-0354378); SyNAPSE program of the Defense Advanced Research Project Agency (HR001109-03-0001); Defense Advanced Research Project Agency (HR001-09-C-0011

Filling-in the Forms: Surface and Boundary Interactions in Visual Cortex

Defense Advanced Research Projects Agency and the Office of Naval Research (NOOOI4-95-l-0409); Office of Naval Research (NOOO14-95-1-0657)

Linking Visual Cortical Development to Visual Perception

Defense Advanced Research Projects Agency and the Office of Naval Research (N00014-95-1-0409); National Science Foundation (IRI-97-20333); Office of Naval Research (N00014-95-1-0657