Gravitational cues contribute to accurate localisation of mentally represented cutaneous targets

The purpose of this research was to ascertain whether gravitational cues contribute to localisation ability of mentally represented cutaneous targets. Eight right-handed male subjects were asked to use each hand to point accurately toward four points in the anterior trunk midline solely on the basis of the mental representation of their position along the trunk while standing upright and while lying supine. It was found that subjects were more accurate when performing in the upright posture. However, statistical analysis of the mean constant transverse errors of pointing showed that neither posture nor target factors had any significant effect on pointing accuracy. On the contrary, analysis of the mean constant longitudinal errors showed that both the posture and target factors were significant. Subjects pointed caudally to the target locations and made the largest errors, which were on the order of centimeters, when performing in the horizontal posture. These findings indicate that gravitational cues are critical in accurately localising mentally represented cutaneous targets.