Chapter Review Summary

The brain is divided into several different structures, but of particular importance for cognitive psychology is the forebrain. In the forebrain, each cerebral hemisphere is divided into the frontal lobe, parietal lobe, temporal lobe, and occipital lobe. In understanding these brain areas, one important source of evidence comes from studies of brain damage, enabling us to examine what sorts of symptoms result from lesions in specific brain locations. This has allowed a localization of function, an effort that is also supported by neuroimaging research, which shows that the pattern of activation in the brain depends heavily on the particular task being performed.

Different parts of the brain perform different jobs, but for virtually any mental process, different brain areas must work together in a closely integrated fashion. When this integration is lost (as it is, for example, in Capgras syndrome), bizarre symptoms can result.

The primary motor projection areas are the departure point in the brain for nerve cells that initiate muscle movement. The primary sensory projection areas are the main points of arrival in the brain for information from the eyes, ears, and other sense organs. These projection areas generally show a pattern of contralateral control, with tissue in the left hemisphere sending or receiving its main signals from the right side of the body, and vice versa. Each projection area provides a map of the environment or the relevant body part, but the assignment of space in this map is governed by function, not by anatomical proportions.

Most of the forebrain’s cortex has traditionally been referred to as the association cortex, but this area is itself subdivided into specialized regions. This subdivision is reflected in the varying consequences of brain damage, with lesions in the occipital lobe leading to visual agnosia, damage in the temporal lobes leading to aphasia, and so on. Damage to the prefrontal area causes many different problems, but these are generally problems in the forming and implementing of strategies.

The brain’s functioning depends on neurons and glia. The glia perform many functions, but the main flow of information is carried by the neurons. Communication from one end of the neuron to the other is electrical and is governed by the flow of ions in and out of the cell. Communication from one neuron to the next is generally chemical, with a neuron releasing neurotransmitters that affect neurons on the other side of the synapse.

One brain area that has been mapped in considerable detail is the visual system. This system takes its main input from the rods and cones on the retina. Then, information is sent via the optic nerve to the brain. An important point is that cells in the optic nerve do much more than transmit information; they also begin the analysis of the visual input. This is reflected in the phenomenon of lateral inhibition, which leads to edge enhancement.

Part of what we know about the brain comes from single-cell recording, which can record the electrical activity of an individual neuron. In the visual system, this recording has allowed researchers to map the receptive fields for many cells, and this mapping has provided evidence for a high degree of specialization among the various parts of the visual system, with some parts specialized for the perception of motion, others for the perception of color, and so on. These various areas function in parallel, and this parallel processing allows great speed; it also allows mutual influence among multiple systems.

Parallel processing begins in the optic nerve and continues throughout the visual system. For example, the what system (in the temporal lobe) appears to be specialized for the identification of visual objects; the where system (in the parietal lobe) seems to tell us where an object is located.

The reliance on parallel processing creates a problem of reuniting the various elements of a scene so that these elements are perceived in an integrated fashion. This is called the binding problem. One key in solving this problem, though, lies in the fact that different brain systems are organized in terms of maps, so that spatial position can be used as a framework for reuniting the separately analyzed aspects of the visual scene.