Cognitive Affective Behavior

Perception Theory The issue of perception in various fields, including philosophy and psychology has been debated with vigor over the last fifty years. In fact, a large amount of experimental work has been completed regarding questions such as the object of perception, the relationship between perception and though, and the nature of perception representational. In general it is believed that perception occurs without apparent effort. What is seen is imposed upon the brain and perception is the natural consequence. Theorists have however argued that this is not the case.

There are a number of factors involved in the perception process. These factors influence the way that objects are perceived. It has for example been argued that perception is a process of information transmission and elaboration. The cognitivist paradigm holds that a flow of information in the mind, similar to computer software, influences the way that objects are perceived. The lines of thought related to visual perception can be divided into the top-down approach, which is concept-driven, and the bottom-up approach, which is direct, and also related to Gibson's view.

The concept-driven approach assumes several information processes within the mind while perception is taking place. Light intensities on the retina are for example assumed to be transformed on the retina in order to perceive the environment. Theories adhering to this principle are known as the constructivist approach. The assumption inherent in the constructivist approach is that several events intervene between stimulation of the perception organs and experience. Inferential processes play a role in forming the internal hypotheses, expectations and knowledge inherent in the final experience related to the vision process.

Furthermore inherent factors such as motivation and emotion are important to the outcome of the process. There are many shortcomings to this approach. Contrary to the prediction that perception is likely to be in error fairly often, studies have shown it to be accurate. Artificial and unnatural stimuli have been used in experiments and demonstrations, rendering these invalid. It appears that the more contemporary approaches to visual perception may therefore offer more in terms of validity.

In order to consider the theory of perception then, Gibson's ecological approach and Marr's computational theory are discussed below. The computational theory appears to oppose the environmental theory in its paradigm that the mind mediates all that is perceived. What is perceived is then influenced by processes in the mind in order to give a message of perception to the brain. This is compared with Gibson's direct approach to vision. J.J.

Gibson and the Ecological Approach to Vision Gibson studied under vision philosophers such as Koffka, while also being influenced by Lewin and Piaget to arrive at his ecological view. He is popularly believed to have coined the term "affordence," and is the founder of the concept of Ecological Perception. The ecological approach suggests a more direct theory. According to this approach, there is no mediation from the mind between the object of perception and the perception event itself. The function of perception is thus one of adaptation.

The purpose of perception is then to adapt the organism to its environment. Gibson's approach is therefore born of the assumption that information within the environment itself, and not in the brain, is sufficient for an organism to move around and interact with the environment. Information is provided by the environment through the direct perception process itself. Organization of action occurs by means of the information derived from the physical environment itself, while action and movement play a role in accurate perception.

The main problem with most theories of visual perception, according to Gibson, is that the phenomenon is considered from a static, abstract perspective. He suggests a more dynamic approach to rectify what he sees as the essential misconception of the perception process. Instead of static, the individual is a moving point in the landscape, or visual array. The environment's layout as it relates to possibilities for action and perception is then seen in terms of its invariant structure.

Gibson assumes that all the visual information emanating from the environment is included in the light pattern reaching the retina. The visual or optical array is therefore supposed to provide unambiguous data regarding what is observed. This information occurs by means of texture gradients, optic floe patterns and affordances. The information is in no way influenced by intermediate information processing. Furthermore Gibson concentrates not on how form itself is perceived, but rather on invariants detected by the visual system. Vision relies on invariants in the dynamic optical array.

The assumption is that environmental surfaces are perceived as a result of such invariants, rather than the form itself. The invariants are then also those of the physical object outside the mind, rather than the images projected on the retina. Gibson referred to the study of these invariants as the Ecological Optic. This is applicable to Gibson's theory on the perception of light. Light cannot actually be seen, but is seen only by means of illuminated objects.

These appear as variations in the environment and are thus able to be seen. Gibson's ecological geometry system describes a world directly perceived by the observer, without any intervention from the faculties of the mind. This perceived world is accurate only to what is directly perceived, and not to any idealism of science such as mathematics. He however does not argue that such mathematically precise distinctions are not possible in a description of the world.

Instead the focus is on the spontaneous, unconscious perception of the world, where such concepts are not used. Thus there is a distinction between the physical properties of the environment in scientific terms, and the way in which the individual experiences the environment. Gibson questions the validity of imposing physical explanations for the world on a description of the world as it appears to its perceiver. Thus Gibson's argument focuses on a misconception of the visual process, rather than erroneous conclusions as a result of this.

He attempts to understand the world through perception as it occurs, rather than through perception as it is imposed upon by learning, thought, or any other mediating processes in the brain. According to Gibson, therefore, development in any visually active organism, from birth to maturity, is a process of distinguishing the physical features of the world around it.

It is thus seen as a learning process through which a seeing person begins to distinguish what is outside of the body, as opposed to a process within the mind by which perception is influenced. The influence of perception thus emerges from the environment outside the seeing person, rather than from the mind. Perception is then, according to Gibson, a process of clarification which is influenced by evolution. The way in which the perception organs develop influences the way that things are seen.

This is also influenced by what is necessary for the survival of a particular organism. Things that are perceived through the senses are specified by way of the light, sound and odor connected with them. Gibson negates all previous and subjective memories as influence on perception. Perception is influenced directly by the environment alone. Gibson expands his theory in relation to 3-dimensional objects. The movement of the perceiver plays a role here.

According to this theory, 3D forms are not perceived through outline with an added form through shading and other such visual cues. Instead they are perceived by the various transformations and relations that shapes undergo as the perceiver moves. This is connected with the view that each eye represents a field of vision. The environment with its potential points of vision are then perceived through both fields of vision to form a 3D image of the environment through which the perceiver moves.

Affordances are explained as the potential use of objects. These, by being perceived directly, provide meaning to the environment. According to Gibson this is also a feature inherent in the evolution process. More than one affordance can be attributed to an object according to the perceiver's species and psychological state. This furthermore substantiates the close connection between perception and action. Meaning according to Gibson is thus located in physical interaction between organism and environment rather than in the mind alone.

Thus information available from the environment relates directly to the meaning derived from perception. It follows that information is energy flowing continuously within the environment and thus from the environment to the physical perception organs of the perceiver. Rather than therefore imposing information upon the environment through the perception process, the function of the brain is to seek information by means of the perception organs and their orientation. Gibson's theories have proved sound for a number of reasons.

In terms of philosophy, Gibson's view brought a new focus to the environment as central to the human experience. When coupled with motion, his contentions regarding the richness of stimuli were shown to be correct. Furthermore his view that inaccurate perception is often the result of artificial situations has also proved accurate. None of the constructivist approaches have proved Gibson's theories incorrect, and in turn Gibson has revealed a number of constructivist fallacies. There are however also shortcomings to Gibson's approach.

The discovery process relating to affordances and invariants in the environment appears to be very complex. He also provides no distinction between "seeing" and "seeing as." Furthermore the complete elimination of an internal representation process combined with the physical act of perception appears extreme and incorrect. It seems that the brain does have a function beyond orienting the perception organs for an optimal perception experience. This is also signified by the cognitive paradigm, and particularly the computational approach proposed by Marr.

Marr's Computational Approach The combined shortcomings of the ecological approach and the constructivist approaches to vision seemed to favor a synthesis of both theories. In this way the shortcomings of each could be cancelled out while the best qualities of each theory could be optimized. The bottom-up approach thus works well in conditions that are favorable for vision, and the top-down theory helps to explain visual perception while viewing conditions are bad, or where there is a lack of clarity in stimulus.

Further important areas of study in the field include eye movement, reaching and grasping, time to contact, and optic flow pattern. Reaching and grasping is dependent on spatial location information, and judgments regarding direction can be made with regard to optic flow pattern. Elements that substantiate Gibson's view of direct vision include decisions regarding time to contact, detection of biological motion, apparent movement and perceived causality. Apparent motion on the other hand does appear to depend on cognitive processes, whether these be low- or high level.

Marr's theory of perception is seen from the neuropsychological level. Marr in fact compares the human visual system to a computer system. Various pathways exist by which the human eye is allowed to perceive. Specialized cells are devoted to conducting the retinal image to the visual centers of the brain. Here the image is processed, and perception occurs.

This indicates the primary function of the brain as a system by which perception occurs, in contrast to the approach by Gibson, which gives the brain only minor functions of movement and orientation. In order to reach a better understanding of the cell system involved in the process of perception, Marr (1982) conducts further investigation of visual perception on a computational level. Marr's investigation leads to three levels of theory in order to understand visual perception in its capacity as a computational device.

Firstly, a computational theory should describe the phenomenon being evaluated and the reason for this evaluation. Secondly, algorithms need to be established in order to achieve the computation, as well as models for the input to and output from the algorithms. Thirdly, the implementation of the algorithms should be explained. In contrast to Gibson, Marr studies the deep recesses of the body in order to come to a conclusion about perception.

This is a very scientific approach, whereas Gibson relied on data gathered from observers and from himself in a more philosophical paradigm. For Marr then a thorough study going beyond the anatomy and physiology of the retinal ganglion cells and lateral geniculate neurons is essential in order to understand the reasons for their receptive fields. Furthermore the connections and interactions of these cells are useful in understanding their behavior.

However in order to understand the reasons for the nature of the receptive fields, it is necessary to study the phenomena of differential operators, band-pass channels, and the mathematics of the uncertainty principle. According to Marr's theory of vision then, the visual image is composed of a wide array of intensity. This could be compared to Gibson's more physical presentation of the optical array, made up of variants. The array of intensity as observed by Marr is created light reflected from observed objects.

When visual perception occurs in its early stages, according to Marr, early visual processing within the brain attempts a description of the perceived object. This is done by the construction of various representations created from the intensity values inherent in the image. This is what Marr refers to as the primal sketch. This sketch includes the description of surfaces and objects, as well as their orientations and distances away from the viewer. This first stage of vision makes local changes in light intensity explicit.

Discontinuities in light intensity are thus located first, and this coincides with important boundaries in the visual scene. Thus the primal sketch is a collection of statements about edges and blobs. Information is given about their whereabouts and orientation, as well as other information for the purposes of visual definition. The following stage then constructs boundaries and regions from the first interpretation by means of application and grouping procedures. The description is then refined, and Marr refers to this as the full primal sketch.

Many of the contours and textures of an image are now perceived, but still only one aspect of early visual processing has developed. Marr saw this model as an observer-orientated representation. He refers to it as the 21/2D sketch, produced by means of motion, depth and shading analysis, as well as a full analysis of the primal sketch. Any action requires the 21/2D sketch as guidance. This is parallel to Gibson's view of the environment and the organism interacting.

The organism observes the environment, and is able to act and move because of this perception. According to Marr a third representational level is necessary for recognition purposes. The observer needs to recognize the object to which a particular shape corresponds. This level is focused on the object, rather than the observer. Gibson's view also is centered on the object of observation, but without applying the complex processes of observation within the body. Marr terms his third level of observation the 3D-model representation.

A number of levels is thus involved in this complex theory of vision. Gibson's theory appears to be one-dimensional, with a variety of components on the same assumed level of vision. Each level in Marr's theory is an increasingly complex and refined symbolic representation of information presented in the retinal image. Each symbolic representation then builds increasing detail into the image towards final recognition and response. This theory therefore proposes vision by means of explicit computation in terms of symbolic description of the image.

The object is recognized when the reconstructed description matches a representation already stored in the brain. The original acquisitions of such stored images are however still questioned. Visual centers in the embryonic brain for example show only instinctive development patterns. This matches a computer before any programs are loaded into it. Marr however does not intend his early processing model to solve visual perception theory problems such as initial image storage.

The goal of his theory is also not to recover the actual object, but rather the initial description of its surfaces, which would then trigger the same stored image already in the mind. This is more or less the same as Gibson's theory, where texture rather than the image itself is used in the construction of an image on the brain. There is thus a relationship for Marr between the light intensity of an image and its surface composition.

Thus changes in intensity provides the observer with important information regarding the geometrical distribution and organization of the object. These physical properties of an object may include depth in visible surfaces, as well as contours and discontinuities. All of these intensity changes then provides the observer with information to decode and identify the object being observed. Changes in intensity are however not only the result of the physical properties of an object. Changes also occur as a result of elements outside of the object.

Shadows passing over the object are an example of this. There must then be a distinction between the features of a scene and the actual image. Visual perception should therefore recreate a representation of the image, and not elements from the scene. Marr also suggests that surfaces can give information through components.