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When we look around in a scene, visual information comes to us only through a series of discrete "snapshots" (i.e., fixations). Why do we not perceive this? Why does it appear that we can "see" the scene in its entirety, smoothly and continuously?
To answer this (and other) questions, experimental psychologists usually begin with one or more theories that explain the phenomena at hand. So what we will do is first specify a theory, generate some hypotheses or predictions that the theory makes, and then we design an experiment to test the hypotheses. This is called the deductive approach, i.e., starting with a theory and then predicting data. (We will illustrate another type of scientific reasoning, an inductive approach, later in this unit).
Integrative Visual Buffer Theory
To begin, the retinal simulation demonstrated what happens on the retina as our eyes move, and we need an explanation of why we are unaware of these events during normal perception. Fortunately we do not have to come up with a theory from scratch. Such a theory already exists that explains why we seem to "see" the world in its entirety, smoothly and continuously. Moreover, it also explains why the world does not appear to 'jump around' despite that the fact the retinal image shifts its position on the retina from one fixation to the next.
This theory, the integrative visual buffer theory (Breitmeyer, 1984) assumes that with each fixation, all the information on our retinae is encoded and stored in a visual buffer. Moreover, all the objects and features represented in this buffer have codes that specify where they are located in the world. Thus we know not only what objects are in the world but also where those objects are in the world. After the saccade, a new part of the world is foveated and information contained in the new retinal image is "integrated" in the visual buffer.
|First, let the picture below represent objects in the world, and assume you first fixate the blue square in the picture below. The red circle is in your peripheral vision.||Second, let the picture below be the imaged objects on your retina. The blue square is at the fovea where it is seen sharp and clear. Because spatial and chromatic resolution falls off rapidly for objects off the fovea, the red circle is distorted.||Third, let the picture below be the contents of the integrative visual buffer. The blurry red circle means that this part of the world is poorly represented compared to the blue square. The X and Y axes represent the location of the objects in the world.|
|Now the red circle is fixated and the blue square is in your periphery.||The red circle is now imaged sharp and clear, this time on the fovea. The blue square is now imaged on a peripheral part of the retina.||The perceptual system now "integrates" this new retinal information into the integrative visual buffer. The sharp, clear red circle means that this part of the world is now clearly represented.|
This theory then proposes that the world appears whole, stable, and continuous, despite foveal limitations and eye-movements, because in our mind's eye a complete visual picture of the world is continuously updated, easily accessible, and perpetually available. In short, our rich, visual, perceptual experience is based on this integrative visual buffer.