Wednesday, December 05, 2007

Emotion as Motion

Richie Davidson and Jeffrey Maxwell do some cute experiments to integrate two different literatures on our approach and withdrawal behaviors. One concerns the localization of approach and avoidance behaviors in the left and right hemispheres, respectively. The lateralization of these processes is very ancient, observed in primitive invertebrates. The other is a description of the general association of flexor (towards the body) movements with approach and extensor (away from the body) movements with avoidance. They do the simple experiment of measuring the reaction time for a subject to point a finger in response to the direction of a flashed image of an arrow pointing away (extension) or towards (flexion).

Legend - Examples of target arrows linked to flexor/extensor movements. On each trial, a single target arrow appeared in either the left or the right target zone (box outline). These target arrows were always flanked by either two diamond distractors or two arrow distractors that fell outside the target zone. Down target arrows pointed both downward and toward the participant. Up target arrows pointed both upward and away from the participant. Down arrows were responded to via finger flexion (i.e., self-directed movements) and up arrows via finger extension (i.e., movements directed away from the self).

The hemispheres were differentially stimulated by presenting the stimuli to either the left (LVF) or right (RVF) visual field. Visual input from the LVF (i.e., the right side of the retinas) projects to visual cortex in the right hemisphere (RH), and visual input from the RVF (i.e., the left side of the retinas) projects to visual cortex in the left hemisphere (LH). Sure enough, facilitation of flexor (compared with approach) responses relative to extensor (compared with avoidant) responses was greater in the LH (i.e., RVF targets) than in the RH (i.e., LVF targets). This pattern of hemispheric specialization was observed to a greater degree the higher participants' self-reported level of daily positive affect and the lower their self-reported level of dispositional anxiety.

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