1630 



IIVXDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY III 



AMBIENT SOUND (SINGLE CLICK) 



+ 5 56° 



AVERAGE CONSTANT ERRORS (IN DEGREES OF ARC) 



APPARENT +< * 

 MID- LINE 

 (IN DEGREES) 



BODY TILTED LEFT (28T 



BODY ERECT 

 ' BODY TILTED RIGHT (28°) 



30°L IO°L IO°R 30°R 

 STARTING POSITION OF SOURCE 



fig. 24. Auditory localization under conditions of body tilt. 

 I' Normal adults set a sound source off to the right when 



tlicv are tilted 30 to their left, and off to the left when they 

 are tilted to their right. Thus, while tilted, the subjective 

 'straitdit overhead' position of the source deviates from its 

 objective overhead position. Below: Plot of mid-line settings 

 (in degrees of arc.) as a function of body position and of starting 

 position of the source. Note that starting a trial by moving tin- 

 source from the subject's left or right results in characteristic 

 starting position errors as long as the subject's body is tilted. 

 'From Teuber & Licbcrt, unpublished observations 



overhead position with consistent errors, so that their 

 settings (lev liic to the righl when they arc tilted to 

 the left, and converse!) (476; see fig. 24). 



The effects vary with age. The compensatory 

 displacement increases progressively in the visual 

 task from ages 6 to 19 as demonstrated bv Wapner & 

 Wernei I ,-•-•!. For the auditor) task, it has been 

 shown hv Liebert & Rudel (323) that the displace- 

 ment grows progressively from o° (at ages 5 to (>i to 

 6° at age 17. These results may be related to the 

 fact that adaptation to bod) lili is more marked in 

 small children and diminishes with aye. Tims, after 

 a bod) tilt of 30' (lasting foi |0 see I, normal y 



old children, blindfolded, consider themselves 

 upright when the) are in fact siill dlicd an average 



of 1 4 to the sitle of their former tilt. This error 

 diminishes to 4 (in the same direction) by age 17. 20 

 The experiments just described all involve locali- 

 zation of stimuli tinder conditions that combine 

 abnormal posture with minimal or absent visual 

 fields. The resulting errors of localization are absent 

 or minimal in a normal visual scene. It must be 

 remembered further that even though posture, in 

 these experiments, deviates from normal (i.e. up- 

 right), the postural system can be assumed to signal 

 its deviation from the gravitational vertical in es- 

 sentially normal fashion. The situation is different 

 when there is misinformation about one's actual 

 posture, as in a centrifuge (or circling aircraft) when 

 the force acting on the body becomes a resultant of 

 gravitational and centrifugal forces. Position of the 

 body and of visual targets [e.g. a collimatcd star in 

 the dark, see Graybiel (169)] are misperceived. 



OCULOGRAVIC effects and related phenomena. 

 Mach (332) thought that these illusions corresponded 

 exactly to the resultant of forces acting on the laby- 

 rinth, but this is not true (543), except (approxi- 

 mately) in a dark room (169). These 'oculogravic 

 effects' are very much diminished in the presence of 

 a patterned visual scene. Similarly, the illusory 

 displacements and drifts of single lights or sounds 

 [the oculogyral effects of Graybiel c< Hupp (170) 

 and the audiogyral effects of Clark & Graybiel (89)], 

 alter acceleration or deceleration, are maximal in an 

 otherwise dark field and reduced under normal 

 v isual stimulation. 



Abnormalities oj Space Perception after Cerebral Lesions 



The complex interaction among sensory (and 

 motor! systems in normal space perception makes it 

 likely that abnormalities after cerebral lesions can 

 take man) forms, differing with the site of the lesion 

 and the tasks employed to demonstrate the deficits. 

 Analysis of these effects is incomplete, even for man, 

 and scarcely begun for infrahuman species (466). 



"The marked adaptation to body tilt in young children 

 may not only be a function ol vestibular adaptation as SUI h 

 In the same scries of experiments, I'eubei \ l.iebert 147b! 

 and l.iebert .X- Rudel (323) showed that young children are 

 more readily influenced by the starting position ol stimuli (535) 

 on a variety of psychophysical tasks thus. In adjusting a (Ink 

 to the overhead position, children will set the sound source 

 sinticuhat to the right, il the trial is begun with the source 

 to their tight, and to the left, with the source starting lo their 

 It ii I Im m 'starting-position effects' diminish progressively 

 with age according to l.iebert & Rudel (393) and Rudel, 

 Teuber & Liebert (manuscript in preparation). 





