BEHAVIOR AND CNS INTEGRATION 201 



viding information about conditionable stimuli (e.g., hue, flicker, frequency, 

 and brightness) which can be differentiated by an unoperated animal during 

 the few seconds, or less, of stimulus presentation. 



A survey of the literature reveals that there have been only a few recorded 

 attempts to classically condition sharks. Karamian (1956) described the first 

 such experiment, carried out by Baru on dogfish in his laboratory. She 

 obtained rapid formation of conditioned responses to light onset, or the 

 sound of a bell, paired with shock; however, in comparison to similar 

 conditioning in teleosts, the shark responses were characteristically unstable. 

 The possibility exists that they may have resulted from improperly 

 controlled nonassociative factors, such as sensitization or pseudo- 

 conditioning, but sufficient procedural details from which to judge are not 

 available. 



The first definitive report on classical conditioning in sharks was recently 

 published by Gruber and Schneiderman (1975). Using restrained young 

 lemon sharks (Negaprion brevirostris), they demonstrated successful condi- 

 tioning of the nictitating membrane response (eye blinking) to a light flash. 

 All animals were conditioned within the first 100-trial session, and, by the 

 second daily session, their performance had stabilized at the 95% level of 

 conditioned responding. Appropriate controls ruled out any possible in- 

 fluence of nonassociative factors. The authors emphasize that the response 

 characteristics resembled those seen in mammals, during both acquisition 

 and extinction. This similarity suggests the future use of conditioning as a 

 tool for comparing sharks with other groups of animals and for studying 

 elasmobranch neurobiological mechanisms, especially central visual process- 

 ing. 



Instrumental Conditioning— Although vision's basic function is to 

 detect photic stimuli, its role is more typically thought to include the guiding 

 of instrumental behavior. Consequently, many investigators employ instru- 

 mental conditioning procedures to study the functional contributions of 

 various central visual system components. Some use traditional training 

 techniques whereby animals are administered a fixed number of trials per 

 day at a predetermined rate, while others use more recently developed 

 operant conditioning methods. In contrast to classical conditioning, both 

 techniques permit the viewing of fairly complex visual stimuli that can be 

 varied according to the timing, patterning, or directionality of light presenta- 

 tion. 



Because learning does not depend on the precise timing of stimulation, the 

 animal has sufficient opportunity to extract relevant stimulus information. 

 By varying response requirements one can also examine how perceived visual 

 information is translated into appropriate action patterns (Schneider 1969). 

 Thus, the investigator can examine responsiveness to a greater range of visual 

 stimuli than is possible using classical conditioning or natural response 

 testing and can obtain a more comprehensive view of surgically induced 

 deficits. 



Here again, progress has been hindered by the common view that sharks 

 are primarily creatures of primitive instinct, practically impossible to train. 



