Question

2. Describe three ways in which the visual system compensates for aspects of the visual stimulus to give us perceptions of a stable, real physical world.

3. What does it mean to assume that the mind is modular? Make sure to clearly distinguish this view from the view that processing structures in the brain are domain general. What evidence supports the modular view and what evidence undermines it?

4. What is difference between bottom-up and top-down processing? Describe in detail an example of each from the theories of visual pattern recognition.

5. What is the difference between an early selection model of attention and a late selection model of attention? Describe an example of each kind of model, including discussing what makes it a model of that type.

Answer 1

• 4.There are two general processes involved in sensation and perception. Bottom-up processing refers to processing sensory information as it is coming in. In other words, if I flash a random picture on the screen, your eyes detect the features, your brain pieces it together, and you perceive a picture of an eagle. What you see is based only on the sensory information coming in. Bottom-up refers to the way it is built up from the smallest pieces of sensory information.
• For example, there is a flower at the center of a person's field. The sight of the flower and all the information about the stimulus are carried from the retina to the visual cortex in the brain. The signal travels in one direction.
• Being a strong support of the bottom up processing approach, Gibson argued that perception is not subject to hypotheses; rather, perception is a direct, "What you see is what you get" phenomenon.
• He explained that our environment can sufficiently supply details related to the stimulus (e.g. size, shape, distance, etc.), so perception of the stimulus may not depend on prior knowledge or past experience.
• Motion parallax supports this argument. When we travel on a fast moving train, we perceive that objects closer to us pass by faster, while farther objects pass us slowly. Thus, we are able to perceive the distance between us and the object that pass us by based on the speed at which they pass.
• Top-down processing is defined as the development of pattern recognition through the use of contextual information. For instance, you are presented with a paragraph written with difficult handwriting.
• It is easier to understand what the writer wants to convey if you read the whole paragraph rather than reading the words in separate terms. The brain may be able to perceive and understand the gist of the paragraph due to the context supplied by the surrounding words.
• In 1970, psychologist Richard Gregory stated that perception is a constructive process that depends on top-down processing. He explained that past experience and prior knowledge related to a stimulus help us make inferences.
• For Gregory, perception is all about making the best guess or a hypothesis about what we see. In terms of visual perception, Gregory argues that about 90% of visual information is lost by the time it arrives in the brain for processing.
• This event leads to the creation of a perceptual hypothesis about the stimulus, based on his memory and past experience that may be related to it.
• When it comes to visual illusions, such as the Necker tube, Gregory believed that the brain may create incorrect hypotheses, leading to several errors of perception.
• The Necker cube is a good example of this. When you stare at the crosses on the cube the orientation can suddenly change, or 'flip'.
• It becomes unstable and a single physical pattern can produce two perceptions.
• Gregory argued that this object appears to flip between orientations because the brain develops two equally plausible hypotheses and is unable to decide between them.
• When the perception changes though there is no change of the sensory input, the change of appearance cannot be due to bottom-up processing. It must be set downwards by the prevailing perceptual hypothesis of what is near and what is far.
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