We identify two aspects of the problem of maintaining perceptual stability despite an observer's eye movements. The first, visual direction constancy, is the (egocentric) stability of apparent positions of objects in the visual world relative to the perceiver. The second, visual position constancy, is the (exocentric) stability of positions of objects relative to each other. We analyze the constancy of visual direction despite saccadic eye movements.Three information sources have been proposed to enable the visual system to achieve stability: the structure (...) of the visual field, proprioceptive inflow, and a copy of neural efference or outflow to the extraocular muscles. None of these sources by itself provides adequate information to achieve visual direction constancy; present evidence indicates that all three are used.Our final question concerns how information processing operations result in a stable world. The three traditionally suggested means have been elimination, translation, or evaluation. All are rejected. From a review of the physiological and psychological evidence we conclude that no subtraction, compensation, or evaluation need take place. The problem for which these solutions were developed turns out to be a false one. We propose a “calibration” solution: correct spatiotopic positions are calculated anew for each fixation. Inflow, outflow, and retinal sources are used in this calculation: saccadic suppression of displacement bridges the errors between these sources and the actual extent of movement. (shrink)

Visual information follows at least two branches in the human nervous system, following a common input stage: a cognitive ''what'' branch governs perception and experience, while a sensorimotor ''how'' branch handles visually guided behavior though its outputs are unconscious. The sensorimotor system is probed with an isomorphic task, requiring a 1:1 relationship between target position and motor response. The cognitive system, in contrast, is probed with a forced qualitative decision, expressed verbally, about the location of a target. Normally, the cognitive (...) system is influenced by context-induced illusions of visual direction, while the sensorimotor system is not. Here, we inquire whether the process of making a spatially based decision is critical in forcing subjects to use the information in the cognitive system for spatial tasks. Subjects hear a tone that determines whether they jab an ''X'' or an ''O'' with the forefinger. Despite making a decision about which target to contact, the jab is not influenced by the position of a surrounding frame, indicating that choice can be handled within the context-insensitive sensorimotor system. (shrink)

Mathematical models are potentially as useful for culture as for evolution, but cultural models must have different designs from genetic models. Social sciences must borrow from biology the idea of modeling, rather than the structure of models, because copying the product is fundamentally different from copying the design. Transfer of most cultural information from brains to artificial media increases the differences between cultural and biological information. (Published Online November 9 2006).

Mirror systems must be supplemented by a planning capability to allow language to evolve. A capability for creating, storing, and executing plans for sequences of actions, having evolved in primates, was applied to sequences of communicatory acts. Language could exploit this already-existing capability. Further steps in language evolution may parallel steps seen in the development of modern children.

The Grand Illusion, the experience of a rich phenomenal visual world supported by a poor internal representation of that world, is echoed by petit illusions of the same sort. We can be aware of several aspects of an object or pattern, even when they are inconsistent with one another, because different neurological mechanisms code the various aspects separately. They are bound not by an internal linkage, but by the structure of the world itself. Illusions exploit this principle by introducing inconsistencies (...) into normally consistent patterns of stimulation. (shrink)

Van Gelder's example of a dynamical model is a Perceptron. The similarity of dynamical models and Perceptrons in turn exemplifies the close relationship between dynamical and algorithmic models. Both are models, not literal descriptions of brains. The brain states of standard modeling are better conceived as processes in the dynamical sense, but algorithmic models remain useful.

Psychology can be based on plans, internally held images of achievement that organize the stimulus-response links of traditional psychology. The hierarchical structure of plans must be produced, held, assigned priorities, and monitored. Consciousness is the operation of the plan-executing mechanism, enabling behavior to be driven by plans rather than immediate environmental contingencies. The mechanism unpacks a single internally held idea into a series of actions. New in this paper is the proposal that language uses this mechanism for communication, unpacking an (...) idea into a series of articulatory acts. Language comprehension uses the plan-monitoring mechanism to pack a series of linguistic events into an idea. Recursive processing results from monitoring one's own speech. Neurophysiologically, the planning mechanism is identified with higher-order motor control. (shrink)

Express saccade experiments imply that attention shifts take time. We extend this result with new experiments on manual reaction times. Reaction to a cued target is always slower than reaction to an uncued control, even when the cue is correct, if control trials are blocked to prevent interference from cued trials. Attention functions not to speed response, but to prevent responses at irrelevant locations.

Hyperbolic theories have the fatal flaw that because of their vertical asymptote they predict irresistible choice of immediate rewards, regardless of future contingencies. They work only for simple situations. Theories incorporating intermediate unconscious choices are more flexible, but are neither exponential nor hyperbolic in their predictions. They don't solve the free will paradox, which may be just a consistent illusion.

The visual system captures a unique contrast between implicit and explicit representation where the same event (location of a visible object) is coded in both ways in parallel. A method of differentiating the two representations is described using an illusion that affects only the explicit representation. Consistent with predictions, implicit information is available only from targets presently visible, but, surprisingly, a two-alternative decision does not disturb the implicit representation.

Both distributed coding, with its implication of neural reuse, and more specialized function have been recognized since the beginning of brain science. A controversy over imageless thought threw introspection into disrepute as a scientific method, making more objective methods dominate. It is known in information science that one element, such as a bit in a computer, can participate in coding many independent states; in this commentary, an example is given.

Although the sensorimotor account is a significant step forward, it cannot explain experiences of entoptic phenomena that violate normal sensorimotor contingencies but nonetheless are perceived as visual. Nervous system structure limits how they can be interpreted. Neurophysiology, combined with a sensorimotor theory, can account for space constancy by denying the existence of permanent representations of states that must be corrected or updated.

Lack of symmetry of stone tools does not require that hominids making asymmetric tools are incapable of doing better. By analogy, differences between stone tools of early humans and modern technology arose without genetic change. A conservative assumption is that symmetry of stone artifacts may have arisen simply because symmetrical tools work better when used for striking and chopping rather than scraping.

The perception/planning–control conception has a direct predecessor in a cognitive/sensorimotor scheme, where the cognitive branch includes Glover's perception and planning functions. The sensorimotor branch corresponds to Glover's control function. The cognitive/sensorimotor scheme, like the perception/planning–control scheme, differentiates between motor planning and direct motor control, which is inaccessible to awareness or to long-term memory.

While the PREDICATE(x) structure requires close coordination of subject and predicate, both represented in consciousness, the cognitive (ventral), and sensorimotor (dorsal) pathways operate in parallel. Sensorimotor information is unconscious and can contradict cognitive spatial information. A more likely origin of linguistic grammar lies in the mammalian action planning process. Neurological machinery evolved for planning of action sequences becomes applied to planning communicatory sequences.

Neuroanatomy and neurophysiology are insufficient to specify function. Modeling is essential to elucidate function, but psychophysics is also required. An example is the cognitive and sensorimotor branches of the visual system: anatomy shows direct cross talk between the branches. Psychophysics in normal humans shows links from cognitive to sensorimotor, but the reverse link is excluded by visual illusions affecting the cognitive system but not the sensorimotor system.

Environment can provide information used in development – information that can appear to be genetically given and that was previously assumed to be so. Examples include growth of the eye until it achieves good focus, and structuring of receptive fields in the visual cortex by environmental information. The process can be called one-generation Lamarckism because information acquired from the environment is used to structure the organism and because the capacity to acquire this information is inherited.

Seemingly small changes in brain organization can have revolutionary consequences for function. An example is evolution's application of the primate action-planning mechanism to the management of communicative sequences. When feedback from utterances reaches the brain again through a mechanism that evolved to monitor action sequences, it makes another pass through the brain, amplifying the human power of thinking.