Conditioned modification of phototactic behavior in Hermissenda. I. Analysis of light intensity.

Psychophysical experiments examined the control of phototactic behavior by light intensity in the nudibranch mollusk Hermissenda by measuring the time that Hermissenda remained in an illuminated area. This measure of phototactic behavior exhibits a closer correspondence to changes in test light intensity than other previously examined measures of phototaxis. Changing the intensity of a test light in a series of increasing steps resulted in a graded increase in positive phototactic behavior. Behavioral responses to different light intensities were examined in conditioned and control animals. Conditioning resulted in a significant suppression of phototactic behavior at all light intensities examined. Random control procedures did not produce suppression of phototactic responding. These behavioral results provide a data base to examine how well neural correlates produced during conditioning fit the behavior.