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

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.     

Effects of response eccentricity and relative position on orthogonal stimulus-response compatibility with joystick and keypress responses

When unimanual left-right movement responses are made to up-down stimuli, performance is better with the up-right/down-left mapping when responding in the right hemispace and with the up-left/down-right mapping when responding in the left hemispace. We evaluated whether this response eccentricity effect is explained best in terms of rotational properties of the hand (the end-state comfort hypothesis) or asymmetric coding of the stimulus and response alternatives (the salient features coding hypothesis). Experiment 1 showed that bimanual keypresses yield a response eccentricity effect similar to that obtained with unimanual movement responses. In Experiment 2, an inactive response apparatus was placed to the left or right of the active response apparatus to provide a referent. For half of the participants, the active and inactive apparatuses were joysticks, and for half they were response boxes with keys. For both response types, an up-right/down-left advantage was evident when the relative position of the active response apparatus was right but not when it was left. That bimanual keypresses yield similar eccentricity and relative location effects to those for unimanual movements is predicted by the salient features coding perspective but not by the end-state comfort hypothesis.     

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

When up-down stimuli are mapped to left-right responses, an up-right/down-left mapping advantage is found that is modified by response eccentricity and hand posture. These effects can be attributed to correspondence of asymmetric stimulus and response codes formed relative to multiple reference frames. We examined the influence of stimulus-set location on these orthogonal stimulus-response compatibility (SRC) effects. In Experiment 1, the stimulus set appeared in the upper or lower display positions. A spatial code for stimulus-set location was formed, producing Simon-type response eccentricity and hand posture effects, but this code had no influence on the coding of the relevant stimuli. In Experiment 2, the stimulus set appeared in the left, center, or right positions relative to the response location, which also varied, to dissociate the effects of response location, relative to the stimulus display and body midline. The former factor influenced the orthogonal SRC effect for both unimanual switch movements and bimanual keypresses, and the latter factor influenced the effect for only unimanual switch movements. Stimulus-set location causes orthogonal Simon-type effects when varied along the stimulus dimension and provides a referent for response coding when varied along the response dimension.     

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

When up-down stimuli are mapped to left-right responses, an up-right/down-left mapping advantage is found that is modified by response eccentricity and hand posture. These effects can be attributed to correspondence of asymmetric stimulus and response codes formed relative to multiple reference frames. We examined the influence of stimulus-set location on these orthogonal stimulus-response compatibility (SRC) effects. In Experiment 1, the stimulus set appeared in the upper or lower display positions. A spatial code for stimulus-set location was formed, producing Simon-type response eccentricity and hand posture effects, but this code had no influence on the coding of the relevant stimuli. In Experiment 2, the stimulus set appeared in the left, center, or right positions relative to the response location, which also varied, to dissociate the effects of response location, relative to the stimulus display and body midline. The former factor influenced the orthogonal SRC effect for both unimanual switch movements and bimanual keypresses, and the latter factor influenced the effect for only unimanual switch movements. Stimulus-set location causes orthogonal Simon-type effects when varied along the stimulus dimension and provides a referent for response coding when varied along the response dimension.     

An explanation of orthogonal S-R compatibility effects that vary with hand or response position: the end-state comfort hypothesis

This study presents an explanation of orthogonal stimulus-response compatibility (SRC) effects that vary with hand or response location: the end-state comfort hypothesis. It posits that responses are spatially transformed and cognitively mapped onto the stimulus dimension according to relative hand posture, thereby mediating the pattern of facilitation and interference in response selection. In the first three experiments, we investigated the eccentricity effect, finding that responses by the left hand in left hemispace are faster with up-left/down-right mapping while responses by the right hand in right hemispace are faster with up-right/down-left mapping (Michaels & Schilder, 1991, Experiment 1). The endstate comfort hypothesis correctly predicted that the eccentricity effect occurred irrespective of the relative position of the stimulus and response device in the sagittal plane (Experiments 1 and 2), and that it reversed when the stimulus-response set was reversed, regardless of the relative position of the stimulus and response device in the fronto-parallel plane (Experiments 2 and 3). Experiment 4 shows a new orthogonal SRC effect that was predicted by the end-state comfort hypothesis. Our results are inconsis tent with other explanations, such as the virtual-lines hypothesis and the salient-features hypothesis.     

S-R compatibilities depend on eccentricity of responding hand

Bauer and Miller (1982) demonstrated that when responding on the body midline with the right hand, subjects react faster when the pairing between horizontally oriented stimuli (an X to the left or right of fixation) and vertically oriented responses (an up or down finger movement) is left-down, right-up (“anti-clockwise”) but when responding with the left hand, the converse pairing was faster. The present experiments tested whether those preferences held for responses other than on the body midline. Unimanual reaction times for clockwise and anti-clockwise S-R pairings were determined for both hands at the midline and 30 and 60 cm to the left or right. Hand position determined both the direction and extent of the compatibility preference; at eccentric positions the right hand preferred clockwise pairings and the left anticlockwise, the converse of that found by Bauer and Miller. The results extend Bauer and Miller's finding, raise problems for theories of S-R compatibility, and further reveal that the state of the action system “sets up” perception.     

Spatial Compatibility Effects With Unimanual and Bimanual Wheel-Rotation Responses: An Homage to Guiard (1983)

ABSTRACT. Y. Guiard (1983) reported a prescient study of compatibility effects in response times for clockwise/counterclockwise wheel rotations to stimuli in left/right locations. Left-right coding of responses predominated in his study, but some results suggested that unimanual versus bimanual operation was also a factor. The authors report 3 experiments directly examining whether there is a difference in spatial compatibility effects obtained with wheel-rotation responses executed bimanually or unimanually (with left or right hand). Adopting a right-to-clockwise or left-to-counterclockwise mapping was advantageous for top, side, and bottom hand placements. This benefit interacted neither with unimanual or bimanual responding nor with the response hand. The results confirm that the critical relation is between the wheel and stimulus position, and is not effector dependent. This finding is in agreement with results from studies using discrete keypress responses, emphasizing that spatial coding of stimuli, actions, and their goals is of central importance in response-selection decisions.     

Hemispace and information control by the two cerebral hemispheres: which interaction?

Two experiments employing subjects with different experience in tactile discrimination (blind and seeing subjects) were carried out to investigate the effect of the space location of stimuli on the information processing activity of the two cerebral hemispheres. An angle discrimination task that yields a right hemisphere superiority was used. In Experiment 1, seeing subjects showed a general superiority of the left hand (right hemisphere) which was more pronounced in the left hemispace with respect to the central and the right hemispace performance. In Experiment 2, blind subjects showed a significant superiority of the left hand in the central and in the left hemispace and no difference between the two hands in the right hemispace. In both experiments hemispace differences were due only to the modification of the left hand (right hemisphere) performance. These results suggest that the hemispace control by the contralateral hemisphere interacts only with the activity of the hemisphere dominant in the information processing.     

Stimulus-response compatibilities between vertically oriented stimuli and horizontally oriented responses: the effects of hand position and posture

Stimulus-response (S-R) compatibility effects between vertically oriented stimuli (above or below fixation) and horizontally oriented responses (left or right switch deflections by a single hand) have been shown to depend both on which hand responds (Bauer & Miller, 1982) and on the location at which the response is made (eccentricity on a frontoparallel line; Michaels, 1989). In the latter study, hand position and hand posture were confounded, so it is unclear which variable determined the compatibility effect. In Experiment 1, the importance of effector position was tested. Vertically oriented stimuli were paired with a horizontal response solicited at different locations but always involving the same hand posture. Compatibility effects emerged, and their direction depended on position. In Experiment 2, the compatibilities were not evident in a simple reaction time paradigm, so the effect was not due to differential ease of responses. In Experiment 3, a change in hand posture (palm up or palm down) at the same location (the body midline) also affected the compatibilities. It was concluded that the S-R compatibility of orthogonally oriented stimuli and responses is influenced by (1) which hand responds, (2) the location of that hand, and (3) its posture. The results imply that both postural and positional states of the action system affect S-R compatibility.     

Stimulus-response compatibility and the motor system

Three experiments examined stimulus-response (S--R) compatibility relationships with the stimulus array perpendicular to the response array. In Experiments I and II, stimuli indicated right and left positions, while the responses were movements up and down. The mapping right/up and left/down was preferable for the right hand, but the reverse mapping was preferable for the left hand. In Experiment III, the stimuli indicated up and down positions, while the responses were movements to the right and left. In this case, the mapping up/left and down/right was preferable for the right hand, and the reverse mapping was preferable for the left hand. The results are most easily explained by assuming that counterclockwise rotational movements are preferable for the right hand, while clockwise is preferable for the left. These preferences are manifest through combinations of implicit movements towards the stimulus and explicit movements towards the response key. This principle is shown to provide a simpler explanation for some previously reported S-R compatibility effects.     

A Referential coding Explanation for Compatibility Effects of Physically Orthogonal Stimulus and Response Dimensions

This study addresses the dependence of compatibility effects on responding hand with horizontally oriented stimuli and vertically oriented responses (H-V effect) and with vertically oriented stimuli and horizontally oriented responses (V-H effect) reported by Bauer and Miller (1982). Experiment 1 replicated the H-V effect. In Experiment 2, the subject was instructed to respond with the hand in line with the response keys. That eliminated the H-V effect. In Experiment 3, the response board was placed to the left or right side of the subject, yielding a considerably reduced H-V effect and a novel compatibility effect dependent on board location. In Experiment 4, the V-H effect was produced when the subject was required to respond with the hand in line with the response keys. With the hand rotated through 90 in Experiment 5, the V-H effect was eliminated, and a main effect of mapping was observed. The results challenge Bauer and Miller's movement-preference hypothesis and support a referential-coding hypothesis proposed by the author. This assumes that response positions are coded in reference to hand posture, so that physically orthogonal stimulus and response dimensions can overlap with respect to their mental representations. The applicability of this hypothesis to other compatibility effects is demonstrated, and its significance for compatibility theories is briefly discussed.     

Influences of response position and hand posture on the orthogonal Simon effect

When lateralized responses are made to the locations of vertically arrayed stimuli, two types of mapping effect have been reported: an overall up–right/down–left advantage and mapping preferences that vary with response position. According to Cho and Proctor's (2003) multiple asymmetric codes account, these orthogonal stimulus–response compatibility effects are due to the correspondence of stimulus polarity and response polarity, as determined by the positions relative to multiple frames of reference. The present study examined these two types of orthogonal compatibility for situations in which participants made left–right responses to the colours of a vertically arrayed stimulus set, and stimulus location was irrelevant. Although a significant orthogonal Simon effect was not evident when responding at a centred, neutral response position, the effect was modulated by response eccentricity (Experiment 2) and hand posture (Experiment 3). These effects are qualitatively similar to those obtained when stimulus location is task relevant. The results imply that, as Proctor and Cho's (2006) polarity correspondence principle suggests, the stimulus polarity code activates the response code of corresponding polarity even when stimulus location is irrelevant to the task.     

S-R compatibility effects due to context-dependent spatial stimulus coding

Responses are faster with spatial S-R correspondence than with noncorrespondence (spatial compatibility effect), even if stimulus location is irrelevant (Simon effect). In two experiments, we sought to determine whether stimuli located above and below a fixation point are coded as left and right (and thus affect the selection of left and right responses) if the visual context suggests such a coding. So, stimuli appeared on the left or right eye of a face’s image that was tilted by 90° to one side or the other (Experiment 1) or varied between upright and 45° or 90° tilting (Experiment 2). Whether stimulus location was relevant (Experiment 1) or not (Experiment 2), responses were faster with correspondence of (face-based) stimulus location and (egocentrically defined) response location, even if stimulus and response locations varied on physically orthogonal dimensions. This suggests that object-based spatial stimulus codes are formed automatically and thus influence the speed of response selection.     

Visual pattern recognition: Size preprocessing re-examined

Template theories of visual pattern recognition assume the operation of preprocessing routines to deal with irrelevancies such as discrepancies in stimulus size. In three experiments where size was an irrelevant dimension, observers classified pairs of forms as either “same” or “different”. In Experiment I, the classification “different” was required when the stimuli shared the same form but a different orientation, and “same” when the stimuli shared the same form and orientation. Under these conditions RT was an increasing function of the magnitude of the size disparity between stimuli with equal slopes for “same” and “different” judgements. In Experiment II, “different” classifications were made to stimuli that had different forms, and “same” to figures with the same form. This stimulus set produced a size disparity function that interacted with response type; “different” responses had a shallower slope. Experiment III consisted of a mixed stimulus set drawn from both Experiment I and II. Stimuli that produced additive effects of size disparity and response type in Experiment I now produced an interaction between these two factors similar to the one observed in Experiment II. The results of these experiments are interpreted as evidence that previous contradictory results reported in the literature stem from differences in the way the stimulus set is constructed, and that size transformations can not be a necessary operation, at least when “different” judgements are made. The results are problematic for the view that size disparity effects in matching tasks are easily interpretable in terms of a primitive size normalization stage that precedes any comparison operations.     

Spatial compatibility effects on the same side of the body midline

Stimulus-response compatibility effects have been hypothesized to result (a) from a subject's innate tendency to respond in the direction of the source of stimulation, (b) from a correspondence between the spatial codes associated with the effector and the stimulus, or (c) from an attentional bias favoring the effector located in the same hemispace as the command signal. Two experiments were conducted to test these three hypotheses. In Experiment 1 the subjects were requested to make unimanual discriminative key-pressing responses to two light stimuli, both appearing to either the right or left of the fixation point. In one condition the two hands were in anatomical position (uncrossed); in the other they were crossed. The procedure of Experiment 2 was similar to that of Experiment 1 with the exception that both hands, always in an uncrossed position, were placed on the same side of the body midline (on the right or left). The results showed that the compatibility effect depends on a correspondence between the spatial codes associated with the location of the effector and the location of the command stimulus.     

A study of the effect of structural information and familiarity in form perception

Two experiments were carried out to investigate the influence of structural information and familiarity on the processing of visual forms. Pairs of “well” structured and nameable and “poorly” structured and non-nameable fragmented forms were employed as stimuli. The effects of structure and familiarity were assessed by manipulating the visual hemifield of presentation and the task. In Experiment 1 stimuli were judged as being either in the same orientation or mirror-reversed, a task that does not require high-level semantic information to be processed. Experiment 2 required physically identical forms to be matched, which may use either physical or name information. In Experiment 1 “same” judgements were equivalent for both types of stimuli, and “different' judgements were longer for the “poorly” structured (non-nameable) forms. In Experiment 2 there was little overall difference between “well” and “poorly” structured forms, though response times to “well” structured (nameable) forms were slowed for right-visual-field presentations. It is suggested that familiarity may not be sufficient to provide a perceptual advantage for nameable forms, as the advantage for nameable stimuli was confined to “same” judgements in Experiment 1 and response times were shorter for non-nameable stimuli in Experiment 2. Rather, performance depends upon factors such as the computation of global shape (due to structural properties of collinearity and closure) and on the use of different kinds or representations (physical versus name) in matching.     

Effects of face and inanimate-object contexts on stimulus–response compatibility

Prior studies have shown that a left–right spatial compatibility effect occurs for vertically oriented stimuli relative to a background context of a face rotated 90° clockwise or counterclockwise from upright. For stimuli presented at the location of the eyes, the mapping of the right eye to a right response and the left eye to a left response, as would be viewed by the participant, yields better performance than does the opposite mapping. An issue of current interest in social cognition is whether animate objects are processed differently from inanimate ones. We investigated this issue in two experiments in which we compared the compatibility effects obtained with inanimate objects to those obtained with animate, face stimuli. The results showed left–right compatibility effects from the participant’s perspective for vehicles and faces from frontal and profile views, as well as for a road sign. Our findings indicate that coding of stimulus location relative to an external frame of reference is not restricted to face backgrounds.     

Orthogonal stimulus–response compatibility effects emerge even when the stimulus position is task irrelevant

The above-right/below-left mapping advantage with vertical stimuli and horizontal responses is known as the orthogonal stimulus–response compatibility (SRC) effect. We investigated whether the orthogonal SRC effect emerges with irrelevant stimulus dimensions. In Experiment 1, participants responded with a right or left key press to the colour of the stimulus presented above or below the fixation. We observed an above-right/below-left advantage (orthogonal Simon effect). In Experiment 2, we manipulated the polarity in the response dimension by varying the horizontal location of the response set. The orthogonal Simon effect decreased and even reversed as the left response code became more positive. This result provides evidence for the automatic activation of the positive and negative response codes by the corresponding positive and negative stimulus codes. These findings extended the orthogonal SRC effect based on coding asymmetry to an irrelevant stimulus dimension.     

Orthogonal stimulus-response compatibility effects emerge even when the stimulus position is task irrelevant

The above-right/below-left mapping advantage with vertical stimuli and horizontal responses is known as the orthogonal stimulus-response compatibility (SRC) effect. We investigated whether the orthogonal SRC effect emerges with irrelevant stimulus dimensions. In Experiment 1, participants responded with a right or left key press to the colour of the stimulus presented above or below the fixation. We observed an above-right/below-left advantage (orthogonal Simon effect). In Experiment 2, we manipulated the polarity in the response dimension by varying the horizontal location of the response set. The orthogonal Simon effect decreased and even reversed as the left response code became more positive. This result provides evidence for the automatic activation of the positive and negative response codes by the corresponding positive and negative stimulus codes. These findings extended the orthogonal SRC effect based on coding asymmetry to an irrelevant stimulus dimension.     

Naming and equivalence: Response latencies for emergent relations

In an attempt to distinguish between associative network and verbal mediation accounts of equivalence formation, three experiments were carried out in which conditional stimulus relations were established and response latencies assessed during tests for emergent relations. In Experiment 1, three groups of adults were trained with six three-member classes of visual stimuli, using different kinds of stimuli for each group: readily nameable pictograms, which were “preassociated” (Group 1); equally nameable but “non-associated” pictograms (Group 2); or non-associated “abstract” stimuli, designed to discourage the use of verbal mediators (Group 3). For those trained with pictograms, equal response latencies were observed on all tested relations, viz. trained associations, symmetry, transitivity, and transitivity with symmetry, but for subjects given abstract stimuli response latencies were greater on tests requiring transitivity. In Experiment 2 this result was replicated with methodological refinements, using only groups trained with preassociated pictograms or abstract stimuli. In Experiment 3 subjects were pretrained to label abstract stimuli with either individual names or class names. Latencies were longer for tests involving transitivity in the case of those subjects using individual names, but equal response latencies were observed on all four types of test for those using class names. The results suggest that equivalence classesMaybe supported by either an associative network or by verbal mediation, depending on stimulus conditions and the subsequent strategies employed by subjects.