Online research in philosophy

What is difficult to imagine is also surprising to perceive. This indicates that active visual imagery is an integral part of active visual perception. Erroneous mental transformations provide clues to prior assumptions in visual imagery, just as visual illusions provide clues to perceptual assumptions. Visual imagery and perception share generic assumptions about invariants in images of rigid objects.

What do we see when we look at someone's expression of fear? I argue that one of the things that we see is fear itself. I support this view by developing a theory of affect perception. The theory involves two claims. One is that expressions are patterns of facial changes that carry information about affects. The other is that the visual system extracts and processes such information. In particular, I argue that the visual system functions to detect the affects of others when they are expressed in the face. I develop my theory by drawing on empirical data from psychology and brain science. Finally, I outline a theory of the semantics of affect perception.

We present work demonstrating that the nature of an object for our visual system depends on the actions we are programming and on the presence of action relations between stimuli. For example, patients who show visual extinction are more likely to become aware of two objects if the objects fall in appropriate visual locations for a common action. This effect of the action relations between objects is modulated both by the familiarity of the positioning of the objects for action, and by the mere possibility of action (the ‘affordance’) between the objects. In addition, the programming of an action to a part of an object alters the representation of that object, making the ‘part’ into the object selected by the visual system. These results point to object coding being a rather flexible process, affected not only by the perceptual properties of stimuli but also by the relations between these properties and action. We discuss the implications for theories of perception as well as considering why action information, in particular, may be important for perception.

I aim to give a new account of picture perception: of the way our visual system functions when we see something in a picture. My argument relies on the functional distinction between the ventral and dorsal visual subsystems. I propose that it is constitutive of picture perception that our ventral subsystem attributes properties to the depicted scene, whereas our dorsal subsystem attributes properties to the picture surface. This duality elucidates Richard Wollheim’s concept of the “twofoldness” of our experience of pictures: the “visual awareness not only of what is represented but also of the surface qualities of the representation.” I argue for the following four claims: (a) the depicted scene is represented by ventral perception, (b) the depicted scene is not represented by dorsal perception, (c) the picture surface is represented by dorsal perception, and (d) the picture surface is not necessarily represented by ventral perception.

The two contrasting theoretical approaches to visual perception, the constructivist and the ecological, are briefly presented and illustrated through their analyses of space and size perception. Earlier calls for their reconciliation and unification are reviewed. Neurophysiological, neuropsychological, and psychophysical evidence for the existence of two quite distinct visual systems, the ventral and the dorsal, is presented. These two perceptual systems differ in their functions; the ventral system's central function is that of identification, while the dorsal system is mainly engaged in the visual control of motor behavior. The strong parallels between the ecological approach and the functioning of the dorsal system, and between the constructivist approach and the functioning of the ventral system are noted. It is also shown that the experimental paradigms used by the proponents of these two approaches match the functions of the respective visual systems. A dual-process approach to visual perception emerges from this analysis, with the ecological-dorsal process transpiring mainly without conscious awareness, while the constructivist-ventral process is normally conscious. Some implications of this dual-process approach to visual-perceptual phenomena are presented, with emphasis on space perception. Key Words: constructivist; dual-process approach; ecological; size perception; space perception; two visual systems; visual perception theories.

The neural substrate of early visual processing in the macaque is used as a framework to discuss recent progress towards a precise anatomical localization and understanding of the functional implications of the syndromes of blindsight, achromatopsia and akinetopsia in humans. This review is mainly concerned with how these syndromes support the principles of organization of the visual system into parallel pathways and the functional hierarchy of visual mechanisms.

Neurophysiological investigations of the visual system by way of single-cell recordings have revealed a hierarchical architecture in which lower level areas, such as the primary visual cortex, contain cells that respond to simple features, while higher level areas contain cells that respond to higher order features apparently composed of combinations of lower level features. This architecture seems to suggest a feed-forward processing strategy in which visual information progresses from lower to higher visual areas. However there is other evidence, both neurophysiological and phenomenal, that suggests a more parallel processing strategy in biological vision, in which top-down feedback plays a significant role. In fact Gestalt theory suggests that visual perception involves a process of emergence, i.e. a dynamic relaxation of multiple constraints throughout the system simultaneously, so that the final percept represents a stable state, or energy minimum of the dynamic system as a whole. A Multi-Level Reciprocal Feedback (MLRF) model is proposed to resolve the apparently contradictory concepts, by proposing a hierarchical visual architecture whose different levels are connected by bi-directional feed-forward and feedback pathways, where the computational transformation performed by the feedback pathway between levels in the hiararchy is a kind of inverse of the transformation performed by the corresponding feed-forward processing stream. This alternative paradigm of perceptual computation accounts in general terms for a number of visual illusory effects, and offers a computational specification for the generative, or constructive aspect of perceptual processing revealed by Gestalt theory.

In this paper we focus on the modularity of visual functions in the human visual cortex, that is, the specific problems that the visual system must solve in order to achieve recognition of objects and visual space. The computational theory of early visual functions is briefly reviewed and is then used as a basis for suggesting computational constraints on the higher-level visual computations. The remainder of the paper presents neurological evidence for the existence of two visual systems in man, one specialized for spatial vision and the other for object vision. We show further clinical evidence for the computational hypothesis that these two systems consist of several visual modules, some of which can be isolated on the basis of specific visual deficts which occur after lesions to selected areas in the visually responsive brain. We will provide examples of visual modules which solve information processing tasks that are mediated by specific anatomic areas. We will show that the clinical data from behavioral studies of monkeys (Ungerleider and Mishkin 1984) supports the distinction between two visual systems in monkeys, the 'what' system, involved in object vision, and the 'where' system, involved in spatial vision.

Norman's aim to reconcile two longstanding and seemingly opposed philosophies of perception, the constructivist and the ecological, by casting them as approaches to complementary subsystems within the visual brain is laudable. Unfortunately, Norman overreaches in attempting to equate direct perception with dorsal/unconscious visual processing and indirect perception with ventral/conscious visual processing. Even a cursory review suggests that the functional and neural segregation of direct and indirect perception is not as clear as the target article would suggest.

Happiness, like other basic emotions, has visual properties that create the conditions for happiness to be perceived in others. This is to say that happiness is perceivable. Its visual properties are to be identified with those facial expressions that are characteristic of happiness. Yet saying that something is perceivable does not suffice for us to conclude that it is perceived. We therefore need to show that happiness is perceived. Empirical evidence suggests that the visual system functions to perceive happiness as well as other basic emotions. Experiences that can be had simply by virtue of how the perceptual system functions are known as observations. I will thus argue that visual experiences in which we become aware of others’ happiness are observations. This approach will provide the necessary conceptual framework to show that we have perceptual knowledge of others’ happiness.