MECHANORECEPTORS AND BEHAVIOR 



357 



permitted a direct approach to the properties of the otolith organs, which in 

 other vertebrates are experimentally unapproachable. In the otic capsule of 

 the ray, Lowenstein and Roberts (1949, 1951) were able to perform a sys- 

 tematic analysis of the end organs. They found that all three organs (the 

 maculae of the utriculus, sacculus, and lagena) responded to linear accelera- 

 tions when exposed to fore-and-aft tilting. The utriculus had the most 

 general response, for the macula sacculi contained gravity receptors only 

 in its posterior portion, with the anterior part responding to vibrations. The 

 otolith organs effectively measured a change in the static position of the 

 labyrinth. Some units discharged maximally when the head was tipped in 

 one direction (Figure 14); others would respond to the opposite movement, 

 while still others discharged whatever the direction of movement. The units 

 of the lagena, however, discharged maximally in the level position, and rapidly 

 adapted if the head deviated from this (Figure 14). 



lOOp 



>• 

 u 

 z 



LU 



z> 

 O 



£ 40h 



upside 

 down 



side up 



normal 



o — O-t- O-O— ( 

 side down 



POSITION 



upside 

 down 



Figure 14 Frequency response (s _1 ) of single units from the utriculus 

 (•) and the lagena (o) of Raja in response to rotation of labyrinth (redrawn 

 from Lowenstein and Roberts 1951a). 



Lowenstein and Roberts (1951) found that units in part of the macula 

 utriculi, the macula sacculi, and the macula neglecta would respond to vibra- 

 tion, following faithfully frequencies up to 120 Hz. The high vibrational 

 sensitivity of the macula neglecta was particularly notable, and these authors 

 suggested that it might be an important organ for sound detection, a role 

 since advocated on anatomical grounds by Tester et al. (1972) and by Fay et 

 al. (1974) who measured the microphonics for this receptor. 



