There are 2 fundamentally opposing theoretical approaches to understanding perception, incorporating (1) the traditional constructivist paradigm and (2) the ecological paradigm. The constructivist perspective, proposed mainly by Helmholtz, Gregory and Rock, holds that perception is essentially a construction of the mind, and is therefore indirect.

That is that in between the optical input and our perception of it, are intervening psychological processes involving mental elaboration.They believe that sensory inputs are not sufficient to mediate perception alone and that something must be added to it before the final perceptual response it achieved. Ecological theorists, on the other hand, and specifically Gibson (1950, 1966, 1979) developed a theory of direct perception that has completely rejected this scientific dogma by showing that perception was not based on sensory inputs or stimuli at all. Instead he claimed that perception was based on ecological information, which is external to the organism.The following essay will highlight the fundamental key components of this revolutionary theory in order to explain why this theory is so radical.

Instead of concentrating on the information-processing going on within individuals as they see, Gibson examined the information that was available to the organism from its environment. His first and major contention was that there was much more information available in the light that psychologists recognised, and that organisms had only to 'pick up' this information (Gibson 1966). According to Gibson the starting point in perception is the ambient optic array.This is due to the fact that light travels in straight lines and so therefore carries information about the environment through which it has travelled. It is the structure in the light extended over space and time that provides direct information about the surfaces, substances and events for an observer (Davids et al, 1992). Surfaces are very important when discussing perception due to their texture gradients.

These gradients are constructed from textured elements, for example different shades of light and they provide important information about depth, shape, size, angle and distance.As an example when we move, whether walking, or driving or flying a plane, the external world changes. Objects get nearer or more distant, and their texture gradients become broader or finer respectively. Gibson's theory considers how people might use dynamic visual information to guide our interactions with the environment. In particular, Gibson discussed the important of optic flow.

This is visual impression we get as we move around. Objects directly in front of us appear stationary, but objects to the side appear to move towards us.The following diagram of an aeroplane's landing approach, illustrates the optical flow field available to the pilot. As a pilot approaches the ground, the surface with which one will eventually land will remain constant, although increasing in size as one approach's. All around that point there will be radial expansion of textures flowing towards one head.

This flow of textures is described as invariant. This concept of invariants, constructed by Gibson, is arguably one of his most profound contributions to psychology.An invariant is defined by the oxford dictionary as something that is always the same or constant. This is also true in regard to direct perception as they are described as 'higher-order properties of patterns of stimulation which remain constant during changes associated with the observer, the environment or both' Gordon (1997). There are two distinct forms of invariants commonly known to the theorists as transformational and structural invariants.

Transformational invariants disclose information about what is happening to any object.They are consistent patterns of change (such as the rule mentioned before that when an object comes closer and closer to the eye it appears proportionally larger. If this rule cannot be applied then either the speed of movement or the actual size of the object has changed. Another example of a transformational invariant is when a rectangle is tilted away from us its projection shape becomes trapezoidal but continues to look rectangular.

The trapezoid is a transformation of the rectangle but there must be something invariant in the shape that allows the observer to perceive it as a tilted rectangle.Structural invariants also play a vital part in direct perception. According to Gordon (1997) they are higher-order patterns or relationships, which remain constant despite changes in stimulation. A relevant example is how we perceive two objects of equal size at different distances from the observer to be in fact the same size. Gibson's answer reflects the importance of the horizon explaining that the ratio of an objects height to the distance between its base and the horizon is invariant across all distances from the viewer (Gordon, 1997).

This example further emphasises the core concept of Gibsonian theory, which maintains that perception is seen as a continuous and mutual relationship between organism and environment. This dynamic relationship is seen to provide the grounds for direct perception of meaning. Gibson's term for this is 'affordance' and is argued to be one of his most radical concepts (Carrello and Turvey). Affordances have been described as higher order patterns of the environment, which enable the perceiver to perform a certain action, for example a cup affords drinking (Gordon, 1997).For different organisms, affordance will differ, such as for a human being, an open stretch of water will afford swimming or immersion, but for a water bug the same stimulus information would afford support (Gibson, 1979). Gibson makes the strong claim that there is information in the light to specify the affordances of the environment (Gibson, 1979).

This is a radical hypothesis, for it implies that 'the values' and 'meanings' of things in the environment can be directly perceived without the need for mediation processes.A final issue to be discussed is the method humans use to detect information. Do they for example, extract the movements of the textured elements at certain moments in time to correlate their speed and direction to detect texture gradients? Gibson says no, he suggests that information pick-up is done through a process of resonance. This means correctly tuning into a particular stimulation in order to perceive an object. Attunement allows an organism to understand the affordances of an object, so they can shape their actions to utilise them properly.Gibson and his followers argue that the response to stimulation is a response involving the entire organism.

They also reiterate the point that the perceiver must persue an active role for extraction of information to be successful. Therefore, from this brief description of the major concepts that typify the ecological approach it is clear that this theory is truly radical indeed. The tenets underlying this theory stand apart from any of the mainstream perceptual theories that have been previously proposed, not only on a psychological level but almost on a philosophical level also.Gibson's theory rests on the concept of 'ecological optics' which he established as a completely new branch of optics, distinct from the traditional optics found in physics.

Moreover, his fundamental concept of the 'optic array' (an alternative to the concept of 'retinal image') and optical flow field are unique and offer a radically different approach as to how we might construe the stimulus for vision. It is clear therefore why Gibsonian's are typically so evangelical about the merits of the ecological approach as the ideas are so new and fresh and completely different to any ideas that have previously been put forward.Furthermore, Gibson's emphasis on ecological components have greatly influenced a number of theorists and has helped the study of perception to shift from laboratory created experiments into external environment analyses. His approach is therefore more ecologically valid than the constructivist paradigm as he examines organisms in their natural external habitat. In conclusion therefore, Gibson's pioneering ecological theory has significantly helped to advance the academic study of perception and remains one of the most powerful and influential perceptual theories to date.