Perception in cognitive psychology

Perception

Within the realm of cognitive psychology, the concept of perception is a controversial topic. Various approaches attempt to explain the concept of perception. Perception involves the" relationship between the observer and the environment (Caird et al., 1995)." For the purposes of this discussion, we will focus on evaluating two fundamental approaches to explaining perception; direct perception and Inferential Theory.

Direct Perception

The first approach that we will evaluate is direct perception theory, also referred to as the ecological approach, which was introduced by Gibson in the 1960's and 1970's. According to Knapp and Robertson (1986) there are several claims that are presented in Gibson's theory of direct perception. Those claims are as follows

Perception of the surroundings is direct and unaffected by images or representations (Knapp and Robertson (1986).

No schemata, form of memory, or other cognitive configuration contributes to perception (Knapp and Robertson (1986).

Information can be found "in the world"(Knapp and Robertson (1986).

Perception occurs as a result of removing invariants from the optic array (Knapp and Robertson (1986).

Perception can be comparable to resonance as opposed to "processing" (Knapp and Robertson (1986).

Properties of the environment, which are directly perceived, include momentous properties reflecting an animal's interests and utilities (Knapp and Robertson (1986).

Computation is not necessary for perception and both hidden and unhidden surfaces can be perceived visually (Knapp and Robertson (1986).

These claims have aided in the formation of Gibson's theory of direct perception. In addition, it has served as thae foundation for many other cognitive theories. According to Warren and Wertheim (1990) the theory of direct perception asserts that the visual world manifests itself as a structured pattern of light. This pattern, usually referred to as the optic array, contains information because it has particular structural features, called invariants. The process of perception is basically understood as a process of picking up these invariants from the optic array. The perception of such dimensions as color, depth, brightness etc., all depend on whether their characteristic invariants are present in the optic array. So too with motion. Object motion, i.e., movement of an object relative to external space, is also revealed by, or, to use Gibson's terms, specified by, particular invariants. For example, in the case where an object moves against a background, the invariant which specifies the motion of the object can be described as: The disappearance of a particular optic structure in the array (specifying the background) along one borderline of a particular area of the array (specifying the object) and its reappearance along the opposite borderline of that area (Warren and Wertheim,1990).

Futhermore the theory asserts that the retinae move in correlation with the visual world (Warren and Wertheim, 1990). As a result of such movement, the visual streaming action of the optic array relative to the retinae is described as the optic flow (Warren and Wertheim, 1990). In addition, these movements of the retinae in space occur because the eyes move with in their orbits, because the head shifts, because the whole observer is in motion, or any comparable combination (Warren and Wertheim, 1990). In Gibson's estimation, these factors are described as self-motion. (Warren and Wertheim, 1990)

In addition, Gibson believed that the optic flow pattern was never composed of invariants which could indicate movement of the visual world (Warren and Wertheim,1990). On the contrary he asserted that the flow pattern consisted only of invariants created the self or egomotion which in turn caused the optic flow pattern (Warren and Wertheim,1990). consequently, such invariants can only identify that particular self- or egomotion (Warren and Wertheim,1990). The authors give an example of this explaining that if, the flow pattern is caused by movements of the eyes, particular invariants are created that specify these eye movements (e.g., the middle area of the array, specifying the nose of the perceiver, moves relative to the outer borderlines of the flow field). When these invariants are picked up, the observer may become aware of his or her own eye movements. Other invariants are created when the flow pattern is caused by head- or egomotion of the observer. The process of picking up these particular invariants from an optic flow pattern (i.e., the process of perceiving eye-, head- or egomovements from optic information) has been termed visual kinesthesis (Warren and Wertheim,1990).

Warren and Wertheim (1990), assert that even though it is understood that both the vestibular and somatosensory systems, also present a percept of head- or egomotion, these systems supply only additional and more often than not duplicate information, which is free from visual kinesthesis (Warren and Wertheim,1990). The authors also explain that afferent (directed toward a central organ) kinesthetic response from the extraocular muscles about oculomotor activity is not present or untrustworthy (Warren and Wertheim,1990). Therefore, if the brain requires information concerning eye movements it can only depend upon visual kinesthesis (Warren and Wertheim,1990).

According to Knapp and Robertson (1986) Gibson's approach theory of direct perception has two main influences upon cognition.

The first influence is that it explains perception in a way that does not require cognitive processes to be brought into perception to elucidate the concept of perception (Knapp and Robertson 1986). The authors also note that many theorists presuppose that cognition is needed in explaining perception (Knapp and Robertson 1986). The second influence of Gibson's theory is that it made pertinent the concept of information pickup (Knapp and Robertson 1986). In doing so, the theory "not only does not utilize cognition to explain perception but extends perception to displace some apparently clear cases of cognition. Finally, there are suggestions of how Gibson's approach can form the foundation for an extended theory of "cognition" with a completely different scheme for classifying "processes" (Knapp and Robertson 1986)."

Inferential Theory

Another approach that is utilized in explaining perception is inferential theory. This theory is often viewed of as the opposite of the direct perception theory. According to Warren and Wertheim (1990) the inferential theory asserts that the perception of motion or stationarity of objects (relative to external space), including the visual world itself, derives from the outcome of a comparison process between two neural signals. One signal, usually referred to as the "retinal signal," consists of retinal afferents in which the movement characteristics of the image across the retinal surface are encoded. The other signal, usually called the "extraretinal signal," encodes how the eyes move (Warren and Wertheim 1990).

The authors assert that once both signals are equivalent to one another the retinal image motion must have been created from the movement of the eyes Warren and Wertheim (1990). Consequently, the perceptual machinery can follow a rule that once the signals are equal object stationarity is perceived, and when those signals are not equal there is a perception of object motion (Warren and Wertheim,1990).

Another article written by Wertheim (1994) asserts that another adaptation of inferential theory presents a model in which the idea of an extra-retinal signal is substituted with a reference signal (Wertheim 1994). Reference signals are unique in that they do not encode the manner in which the eyes move in their orbits, instead they encode the manner in which they move in space (Wertheim 1994). For this reason, reference signals are formed not just for the duration of eye movements but also during ego-motion (Wertheim 1994). For instance, Wertheim (1994) explains that when a smooth pursuit eye movement is made across a visual stimulus pattern, the magnitude of the retinal signal corresponds to the velocity of the retinal image flow of the pattern. Similarly, the magnitude of the extraretinal signal corresponds to the velocity of the concurrent eye movements as "estimated" within the perceptual apparatus (Wertheim 1994))."

Criticisms associated with both theories

According to (Wertheim,1994) both theories can be problematic in certain sitiuations. The authors present an example using the vection that is produced by an optokinetic drum. They explain that if the drum rotates with an angular velocity of 60 deg/sec around a stationary observer whose body, head and eyes are fixed in space and the lights inside the drum are extinguised, i.e. The observer sits in the dark and does not know that the drum rotates. If we now suddenly switch on the lights inside the drum, the observer will initially perceive the drum correctly as rotating and experience no ego-rotation. However, within a few seconds an illusory sensation of ego-rotation in the direction opposite to that of the drum (called circularvection) gradually develops. During this period ego-velocity is experienced as increasing and the rotation of the drum appears to slow down. Finally, the drum is perceived as completely stationary in space and ego-velocity does not seem to increase any further (Wertheim,1994)."

The criticism in the theories lies in the belief that neither of these approaches can explain why the perception of the drum is that it is a stationary object (Wertheim,1994). In the case of the direct perception theory the drum is perceived as stationary initially because of the awareness of ego- motion and not of motion of the drum (Wertheim,1994). This explanation is problematic because once the rotation of the drum slows down the invariant disappears (Wertheim,1994). On the other hand the inferential theory asserts that moving retinal image creates a retinal signal, however when the eyes are stationary they create a zero extraretinal signal (Wertheim,1994). Thus, because the two signals are not equal and the drum is seen to move (Wertheim,1994). Consequently, when using the inferential theory of perception the criticism is that the drum appears to be stationary even after once vection is saturated (Wertheim,1994).