Eugene Pak


A population of cells responsive to the decrease or dimming of light was identified in the Purple shore crab Hemigrapsus nudus. Extracellular pin electrode recordings from the optic nerve tract measured responses to decremental changes in relative light levels over the range 40 to 0.08 lux. The observed activity revealed that these dimming cells could respond over this entire range. A catalog detailing the response characteristics for each of the thirty dimming cells in the study was generated. The parameters measured the receptive field size; response to mechanoreceptive tactile stimuli; response to abrupt On or Off light level changes; response to object movement; and any changes in the dimming activity.

The results indicate that Hemigrapsus nudusdimming cells comprise a number of response subgroups, in addition to the observed dimming response. The majority of dimming cells (n=20) shared a whole eye receptive field, and all cells detected small changes or jitter in an object's spatial position. Dimming cells were found to respond to light termination only (n=12), or to both light termination and onset (n=9); no cells had a greater response for light onset than for its termination. The study population suggested that dimming cells had multimodal properties, since all cells responded to both tactile and visual stimuli. There also is evidence that some cells had regions of increased sensitivity to certain light levels that were more prominent than for the rest of its response range. Dimming cells with enhanced ranges were separated based on the extent of the increased sensitivity into Brief Range (BR) and Extended Range (ER) responses. BR cells had enhanced responses at very specific light levels; ER cells responded over a portion of their total response range.

Dimming cell responses increased in number with decreasing light levels for almost all response groups. The only exception was for dimming cells responding to light Off only; these cells maintained a constant population (n=12) over all light levels measured. Dimming cells appear important for object movement detection rather than for feature perception in low light environments.

LLU Discipline





Graduate School

First Advisor

Donald D. Rafuse

Second Advisor

Robert A. Chilson

Third Advisor

Conrad D. Clausen

Degree Name

Master of Science (MS)

Degree Level


Year Degree Awarded


Date (Title Page)




Library of Congress/MESH Subject Headings

Crabs -- Physiology; Light -- Physiological effect; Eye -- Adaptation.



Page Count

iv; 47

Digital Format


Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.


Loma Linda University Electronic Theses and Dissertations

Collection Website


Loma Linda University. Del E. Webb Memorial Library. University Archives