Influences of hand posture and hand position on compatibility effects for up-down stimuli mapped to left-right responses: Evidence for a hand referent hypothesis

Abstract

Unimanual left-right responses to up-down stimuli show a stimulus-response compatibility (SRC) effect for which the preferred mapping varies as a function of response eccentricity. Responses made in the right hemispace and, to a lesser extent, at a midline position, are faster with the up-right/down-left mapping than with the up-left/down-right mapping, but responses made in the left hemispace are faster with the up-left/down-right mapping. Also, for responses at the midline position, the preferred mapping switches when the hand is placed in a supine posture instead of the more usual prone posture. The response eccentricity effect can be explained in terms of correspondence of asymmetrically coded stimulus and response features, but it is not obvious whether the hand posture effect can be explained in a similar manner. The present study tested the implications of a hypothesis that the body of the hand provides a frame of reference with respect to which the response switch is coded as left or right. As was predicted by this hand referent hypothesis, Experiment 1 showed that the influence of hand posture (prone and supine) on orthogonal SRC was additive with that of response location. In Experiment 2, the location of the switch relative to the hand was varied by having subjects use either a normal grip in which the switch was held between the thumb and the index finger or a grip in which it was held between the little and the ring fingers. The magnitudes of the mapping preferences varied as a function of the grip and hand posture in a manner consistent with the hand referent hypothesis.

Influences of multiple spatial stimulus and response codes on orthogonal stimulus—response compatibility

“…As in Cho and Proctor's (2002) Experiment 1, this orthogonal SRC effect for RT was influenced independently by response eccentricity and hand posture. The up-right /down-left advantage was larger when subjects responded in the right hemispace than at midline, and it reversed to an up-left /down-right advantage in the left hemispace.…”

“…Thus, stimulusset location and the location of the imperative stimulus influenced the response-selection process in an independent but similar manner. This result also indicates that, like the multiple spatial codes for response location, multiple spatial codes for stimulus location are formed relative to available reference frames and affect response selection additively (e.g., Cho & Proctor, 2002;Lamberts et al, 1992;Proctor & Pick, 1999).…”

“…Cho and Proctor (2003) elaborated this position in what we will call the multiple asymmetric codes account. One fundamental tenet of this account is that spatial codes for the response location are formed relative to available reference frames, including the stimulus display (Cho & Proctor, in press-a), another response apparatus Weeks et al, 1995), and the main part of the responding hand (Cho & Proctor, 2002). The other fundamental tenet of this account is correspondence of asymmetric codes, as specified in Weeks and Proctor's (1990) salient features coding account: Within each reference frame, the polarity is positive for the response code that is consistent with the representation of the response position as left or right, and the polarity is negative for the response code that is inconsistent with this representation.…”

“…This result pattern is counter to the implication of the end-state comfort hypothesis that the orthogonal SRC effect is due to interplay of the responding hand and hand position. Moreover, Cho and Proctor (2002) showed in their Experiment 2 that the hand posture effect obtained by grasping with the thumb and index finger was significantly decreased when subjects grasped a toggle switch with their ring and small fingers. The results of the two experiments imply that the hand posture effect is due at least in part to the coding of response position, and that multiple spatial codes for the response position are formed relative to available reference frames, with their effects combining in a relatively independent manner.…”

“…In Cho and Proctor's (2002) Experiment 1, subjects made left-right toggle-switch movements at three response positions in two hand postures, prone and supine. Response position and hand posture affected the orthogonal SRC effect in an additive manner.…”