| Chapter 3: Perception The visual cortex only receives a fraction of the visual input from the environment. This is called compression. Rods are mainly present in peripheral vision. Hundreds or even thousands of them may be connected to a single bipolar cell, which explains why we do not have fine vision in our periphery. Cones are tightly packed in the fovea and can have a one-on-one connection with a bipolar cell, thus leading to very fine vision. Although we have a continuous, coherent perception of the world, our eyes move by saccadic, jerky movements. We uptake visual information during fixations, especially during the first 50 ms. The fact that we uptake only brief clips of information interrupted by saccades requires us to have a sensory memory that allows the combination of these different clips. Sperling did a lot of research on sensory memory. He found that, using the whole report technique, participants would recall only 4 or 5 letters or digits. This is congruent with the idea that we have a span of apprehension that allows us to take in 4 or 5 items in parallel into the processing system. By using the partial report technique, Sperling showed that the entire matrix was actually present in sensory memory for a short time. |
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