The Two Modes Discovered Again

The two modes of thought were rediscovered again in the 1990s. Raichle (1994), writing in the Annual Reviews of Psychology, reviewed evidence from brain scanning experiments and concluded there were two distinct processing pathways in the brain. One pathway tended to be active during the conscious phase of learning, another during unconscious or automatic processing. Raichle's conscious process corresponds to Neisser's serial process or Bruner's analytic process. Raichle's automatic process corresponds to Neisser's parallel process or Bruner's intuitive process. The names change, but the distinction remains the same.

How were "two modes of thought" discovered again in the 1990s? Which mode is "the head" and which is "the heart"?

Similarly, Epstein (1995) wrote in American Psychologist that evidence points toward "two...modes of information processing: a rational system and an emotionally driven experiential system." He cited many different studies suggesting a "convergence of a wide variety of theoretical positions" that supported the distinction. He also used popular language to describe the distinction, referring to "conflicts between the heart and the head." One system is active during conscious, controlled, or intellectual activity (the head), the other during unconscious, unwilled, emotional responses (the heart).

What is evidence of "two modes of processing" from the study of facial blindness?

The two modes of consciousness can be doubly dissociated like other distinct brain processes. In other words, brain injury can knock out one type of process while leaving the other undamaged.

This can happen with the syndrome called prosopagnosia or facial blindness. Some brain damaged patients cannot consciously recognize any face, including their own or that of the examiner. Yet they show an unconscious emotional response to familiar faces, when monitored by an apparatus similar to a lie detector. The "heart" recognizes the familiar face, although the "head" does not. Other brain-damaged patients show the exact opposite pattern: they show no emotional reaction to a familiar face, but they consciously recognize faces and can name them (Newcombe & Lie, 1995).

Yet another example involves fear conditioning. When a tone is presented before an electric shock several times, normally two consequences occur:

1. The subject has a conscious memory of the task. For example, the subject can tell you about participating in the experiment.

2. The subject shows an emotional (autonomic) response to the tone which came before the shock, as measured on a device resembling a lie detector. For example, if the tone is sounded at a random time, the needles jump.

What is evidence for two modes of processing from the study of fear conditioning?

Bechara, Tranel, Damasio, Adolphs, Rockland, and Damasio (1995) found that these responses, too, could be doubly dissociated. They found one patient with damage near the amygdala, which as you may recall is involved in responses such as fear and rage. The patient with amygdalar damage remembered the fact that a loud horn was sounded before each electric shock but showed no emotional reaction to the horn.

Another patient had damage to the hippocampus, an area involved in creating conscious memories. He showed an emotional reaction to the horn, but he was unable to recall that it had been paired with a shock. Finally, a third patient, with damage to both the amygdala and hippocampus, "acquired neither the [emotional] conditioning nor the facts."

If the two processes can be doubly dissociated, each eliminated without affecting the other, then they represent different processes in the nervous system. This supports Neisser's insight (and everybody else who had the same insight). There is a fundamental difference between consciously remembered, intellectual, controllable mental processes (on the one hand) and unconscious, emotional, automatic reactions (on the other).

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Copyright © 2007 Russ Dewey