Spatial constraints on visual-tactile cross-modal distractor congruency effects

Across three experiments, participants made speeded elevation discrimination responses to vibrotactile targets presented to the thumb (held in a lower position) or the index finger (upper position) of either hand, while simultaneously trying to ignore visual distractors presented independently from either the same or a different elevation. Performance on the vibrotactile elevation discrimination task was slower and less accurate when the visual distractor was incongruent with the elevation of the vibrotactile target (e.g., a lower light during the presentation of an upper vibrotactile target to the index finger) than when they were congruent, showing that people cannot completely ignore vision when selectively attending to vibrotactile information. We investigated the attentional, temporal, and spatial modulation of these cross-modal congruency effects by manipulating the direction of endogenous tactile spatial attention, the stimulus onset asynchrony between target and distractor, and the spatial separation between the vibrotactile target, any visual distractors, and the participant’s two hands within and across hemifields. Our results provide new insights into the spatiotemporal modulation of crossmodal congruency effects and highlight the utility of this paradigm for investigating the contributions of visual, tactile, and proprioceptive inputs to the multisensory representation of peripersonal space.     

Vision of a pictorial hand modulates visual-tactile interactions

The participants in this study discriminated the position of tactile target stimuli presented at the tip or the base of the forefinger of one of the participants’ hands, while ignoring visual distractor stimuli. The visual distractor stimuli were presented from two circles on a display aligned with the tactile targets in Experiment 1 or orthogonal to them in Experiment 2. Tactile discrimination performance was slower and less accurate when the visual distractor stimuli were presented from incongruent locations relative to the tactile target stimuli (e.g., tactile target at the base of the finger with top visual distractor) highlighting a cross-modal congruency effect. We examined whether the presence and orientation of a simple line drawing of a hand, which was superimposed on the visual distractor stimuli, would modulate the cross-modal congruency effects. When the tactile targets and the visual distractors were spatially aligned, the modulatory effects of the hand picture were small (Experiment 1). However, when they were spatially misaligned, the effects were much larger, and the direction of the cross-modal congruency effects changed in accordance with the orientation of the picture of the hand, as if the hand picture corresponded to the participants’ own stimulated hand (Experiment 2). The results suggest that the two-dimensional picture of a hand can modulate processes maintaining our internal body representation. We also observed that the cross-modal congruency effects were influenced by the postures of the stimulated and the responding hands. These results reveal the complex nature of spatial interactions among vision, touch, and proprioception.     

On the inability to ignore touch when responding to vision in the crossmodal congruency task

We investigated the extent to which people can selectively ignore distracting vibrotactile information when performing a visual task. In Experiment 1, participants made speeded elevation discrimination responses (up vs. down) to a series of visual targets presented from one of two eccentricities on either side of central fixation, while simultaneously trying to ignore task-irrelevant vibrotactile distractors presented independently to the finger (up) vs. thumb (down) of either hand. Participants responded significantly more slowly, and somewhat less accurately, when the elevation of the vibrotactile distractor was incongruent with that of the visual target than when they were presented from the same (i.e., congruent) elevation. This crossmodal congruency effect was significantly larger when the visual and tactile stimuli appeared on the same side of space than when they appeared on different sides, although the relative eccentricity of the two stimuli within the hemifield (i.e., same vs. different) had little effect on performance. In Experiment 2, participants who crossed their hands over the midline showed a very different pattern of crossmodal congruency effects to participants who adopted an uncrossed hands posture. Our results suggest that both the relative external location and the initial hemispheric projection of the target and distractor stimuli contribute jointly to determining the magnitude of the crossmodal congruency effect when participants have to respond to vision and ignore touch.     

Within-hemifield posture changes affect tactile–visual exogenous spatial cueing without spatial precision,especially in the dark

We investigated the effects of seen and unseen within-hemifield posture changes on crossmodal visual–tactile links in covert spatial attention. In all experiments, a spatially nonpredictive tactile cue was presented to the left or the right hand, with the two hands placed symmetrically across the midline. Shortly after a tactile cue, a visual target appeared at one of two eccentricities within either of the hemifields. For half of the trial blocks, the hands were aligned with the inner visual target locations, and for the remainder, the hands were aligned with the outer target locations. In Experiments 1 and 2, the inner and outer eccentricities were 17.5º and 52.5º, respectively. In Experiment 1, the arms were completely covered, and visual up–down judgments were better when on the same side as the preceding tactile cue. Cueing effects were not significantly affected by hand or target alignment. In Experiment 2, the arms were in view, and now some target responses were affected by cue alignment: Cueing for outer targets was only significant when the hands were aligned with them. In Experiment 3, we tested whether any unseen posture changes could alter the cueing effects, by widely separating the inner and outer target eccentricities (now 10º and 86º). In this case, hand alignment did affect some of the cueing effects: Cueing for outer targets was now only significant when the hands were in the outer position. Although these results confirm that proprioception can, in some cases, influence tactile–visual links in exogenous spatial attention, they also show that spatial precision is severely limited, especially when posture is unseen.     

Linguistic and Perceptual Mapping in Spatial Representations: An Attentional Account

Building on evidence for embodied representations, we investigated whether Spanish spatial terms map onto the NEAR/FAR perceptual division of space. Using a long horizontal display, we measured congruency effects during the processing of spatial terms presented in NEAR or FAR space. Across three experiments, we manipulated the task demands in order to investigate the role of endogenous attention in linguistic and perceptual space mapping. We predicted congruency effects only when spatial properties were relevant for the task (reaching estimation task, Experiment 1) but not when attention was allocated to other features (lexical decision, Experiment 2; and color, Experiment 3). Results showed faster responses for words presented in Near‐space in all experiments. Consistent with our hypothesis, congruency effects were observed only when a reaching estimate was requested. Our results add important evidence for the role of top‐down processing in congruency effects from embodied representations of spatial terms.     

Visuo-tactile links in covert exogenous spatial attention remap across changes in unseen hand posture

We investigated the effect of unseen hand posture on cross-modal, visuo-tactile links in covert spatial attention. In Experiment 1, a spatially nonpredictive visual cue was presented to the left or right hemifield shortly before a tactile target on either hand. To examine the spatial coordinates of any cross-modal cuing, the unseen hands were either uncrossed or crossed so that the left hand lay to the right and vice versa. Tactile up/down (i.e., index finger/thumb) judgments were better on the same side of external space as the visual cue, for both crossed and uncrossed postures. Thus, which hand was advantaged by a visual cue in a particular hemifield reversed across the different unseen postures. In Experiment 2, nonpredictive tactile cues now preceded visual targets. Up/down judgments for the latter were better on the same side of external space as the tactile cue, again for both postures. These results demonstrate cross-modal links between vision and touch in exogenous covert spatial attention that remap across changes in unseen hand posture, suggesting a modulatory role for proprioception.     

Crossmodal links between vision and touch in covert endogenous spatial attention

The authors report a series of 6 experiments investigating crossmodal links between vision and touch in covert endogenous spatial attention. When participants were informed that visual and tactile targets were more likely on 1 side than the other, speeded discrimination responses (continuous vs. pulsed, Experiments 1 and 2; or up vs. down, Experiment 3) for targets in both modalities were significantly faster on the expected side, even though target modality was entirely unpredictable. When participants expected a target on a particular side in just one modality, corresponding shifts of covert attention also took place in the other modality, as evidenced by faster elevation judgments on that side (Experiment 4). Larger attentional effects were found when directing visual and tactile attention to the same position rather than to different positions (Experiment 5). A final study with crossed hands revealed that these visuotactile links in spatial attention apply to common positions in external space.     

Mislocalizations of touch to a fake hand

Observers can mislocalize a tactile target delivered to an unseen hand if a visible rubber glove is positioned next to a pair of distractor lights that flash in correlation with the tactile target (Pavani, Spence, & Driver, 2000). In the present study, we explored visual, tactile, and postural factors that influence this fake hand effect. Comparison with baseline conditions revealed that the fake hand effect was larger than a general spatial congruity effect but weaker than the effect obtained when tactile and visual stimuli were actually in the same locations (Experiment 1). Surprisingly, the effect did not depend on direct vision of the fake hand (Experiments 1 and 2), nor was it enhanced by congruent tactile information (Experiment 3). However, the fake hand effect was sensitive to the postural compatibility of the real and the fake hands (Experiment 4). These findings indicate that the available sensory information is used flexibly to incorporate the rubber glove into the body schema.     

The role of working memory in tactile selective attention

Load theory suggests that working memory controls the extent to which irrelevant distractors are processed (e.g., Lavie, Hirst, De Fockert, & Viding, 2004). However, so far this proposal has only been tested in vision. Here, we examine the extent to which tactile selective attention also depends on working memory. In Experiment 1, participants focused their attention on continuous target vibrations while attempting to ignore pulsed distractor vibrations. In Experiment 2, targets were always presented to a particular hand, with distractors being presented to the other hand. In both experiments, a high (vs. low) load in a concurrent working memory task led to greater interference by the tactile distractors. These results establish the role of working memory in the control of tactile selective attention, demonstrating for the first time that the principles of load theory also apply to the tactile modality.     

A cross-modal interference effect in grasping objects

The aim of the present paper was to investigate how the kinematics of a hand reaching toward a visual target would be influenced by haptic and proprioceptive input from an unseen distractor actively grasped in the other, nonreaching hand. The main results were that the amplitude of maximum grip aperture was smaller and the time to maximum grip aperture was earlier when the distractor was smaller than the target. The interference effect from the distractor was similar for both hands as they reached. Furthermore, results from a vibrating-distractor condition for passive tactile input revealed that the interference effects were evident only when the distractor was actively grasped. We suggest that neural processing of proprioceptive and tactile information relevant to distractor size produced the observed interference effects. We also emphasize the importance of active manipulation of the distractor stimulus in eliciting such interference effects.     

Hand Position and Response Assignment Modulate the Activation of the Valence‐Space Conceptual Metaphor

Conceptual metaphor is ubiquitous in language and thought, as we usually reason and talk about abstract concepts in terms of more concrete ones via metaphorical mappings that are hypothesized to arise from our embodied experience. One pervasive example is the conceptual projection of valence onto space, which flexibly recruits the vertical and lateral spatial frames to gain structure (e.g., good is up ‐bad is down and good is right ‐bad is left ). In the current study, we used a valence judgment task to explore the role that exogenous bodily cues (namely response hand positions) play in the allocation of spatial attention and the modulation of conceptual congruency effects. Experiment 1 showed that congruency effects along the vertical axis are weakened when task conditions (i.e., the use of vertical visual cues, on the one hand, and the horizontal alignment of responses, on the other) draw attention to both the vertical and lateral axes making them simultaneously salient. Experiment 2 evidenced that the vertical alignment of participants’ hands while responding to the task—regardless of the location of their dominant hand—facilitates the judgment of positive and negative‐valence words, as long as participants respond in a metaphor–congruent manner (i.e., up responses are good and down responses are bad). Overall, these results support the claim that source domain representations are dynamically activated in response to the context and that bodily states are an integral part of that context.     

Tactile orientation constancy: Do proprioception and attention affect the tactile vertical?1

Abstract: Tactile vertical, defined as the edge orientation that participants perceive to be vertical, was examined in four experiments. In Experiment 1, we touched the participants’ cheek, lips, or hand with an edge and asked them to judge its orientation with regard to gravitational vertical, both when the stimulated body part was upright (or, in the case of the lips, aligned), and when it was tilted (lips, distorted). We found that when the head or hand was tilted forward 30°, or when the lower lip was distorted approximately 38° to the left or right, the tactile vertical shifted in the same direction by only a fraction (8.7, 8.6, and 36.3% for the cheek, lips, and hand, respectively) of the change in orientation of the stimulated region. The results indicated considerable, but usually incomplete, orientation constancy. In Experiment 2, we measured tactile vertical on the hand for forward tilts from 0° to 45°. We found that as the hand was tilted, the tactile vertical increasingly shifted in the same direction as the hand (i.e., a tactile Aubert effect). In Experiment 3, the effect of attentional focus on tactile vertical was examined by comparing the tactile vertical of participants who attended to body‐centered coordinates, and others who attended to gravitation‐centered coordinates. We found that focusing on body‐centered coordinates caused a decrease in orientation constancy. We sought to examine the role of attention further in Experiment 4, measuring tactile vertical on the cheek of persons with temporomandibular disorders. Compared with normal participants, these participants displayed significantly lower constancy. The results were accounted for by a narrowing of attention to painful signals, so that proprioceptive information was attended to less. In conclusion, the degree of tactile orientation constancy that participants demonstrate varies as a function of body site and attentional focus.     

Congruency effects between auditory and tactile motion: Extending the phenomenon of cross-modal dynamic capture

Behavioral studies of multisensory integration in motion perception have focused on the particular case of visual and auditory signals. Here, we addressed a new case: audition and touch. In Experiment 1, we tested the effects of an apparent motion stream presented in an irrelevant modality (audition or touch) on the perception of apparent motion streams in the other modality (touch or audition, respectively). We found significant congruency effects (lower performance when the direction of motion in the irrelevant modality was incongruent with the direction of the target) for the two possible modality combinations. This congruency effect was asymmetrical, with tactile motion distractors having a stronger influence on auditory motion perception than vice versa. In Experiment 2, we used auditory motion targets and tactile motion distractors while participants adopted one of two possible postures: arms uncrossed or arms crossed. The effects of tactile motion on auditory motion judgments were replicated in the arms-uncrossed posture, but they dissipated in the arms-crossed posture. The implications of these results are discussed in light of current findings regarding the representation of tactile and auditory space.     

Effects of Expectancy and Attention in Vibrotactile Choice Reaction Time Tasks

The orienting of attention in space has not been considered in the tactile domain. This issue is examined using a modified version of a visual paradigm initially adopted by Posner, Snyder, and Davidson (1980), which manipulates the probability of a stimulus occurring at different spatial locations. Slower RTs at an unexpected stimulus location are thought to reflect the time required to shift attention from the expected to the unexpected location. In two experiments involving vibrotactile choice RT between left and right hands, the two hands were either crossed or uncrossed, and the hands were held both on the left side of the body, both on the right, or one on either side of the midline. There was no evidence to suggest that spatial location (left or right) affected the orienting of attention in the tactual modality. As predicted, RTs were slower when the arms were crossed compared with uncrossed, though this effect was smaller for the expected trials. A coding conflict hypothesis may explain both these findings, but the smaller effect in the expected trials may also reflect attentional factors. Both the relative and absolute location of the hands affected the magnitude of the crossed-arm effect and indicated that attention may play a role in the perceptual division of space into left and right sides. Possible reasons for hand or hemispace asymmetries in different simple and choice RT paradigms were discussed.     

Spatial specificity of tactile enhancement during reaching

Tactile signals on a hand that serves as movement goal are enhanced during movement planning and execution. Here, we examined how spatially specific tactile enhancement is when humans reach to their own static hand. Participants discriminated two brief and simultaneously presented tactile stimuli: a comparison stimulus on the left thumb or little finger from a reference stimulus on the sternum. Tactile stimuli were presented either during right-hand reaching towards the left thumb or little finger or while holding both hands still (baseline). Consistent with our previous findings, stimuli on the left hand were perceived stronger during movement than baseline. However, tactile enhancement was not stronger when the stimuli were presented on the digit that served as reach target, thus the perception across the whole hand was uniformly enhanced. In experiment 2, we also presented stimuli on the upper arm in half of the trials to reduce the expectation of the stimulus location. Tactile stimuli on the target hand, but not on the upper arm, were generally enhanced, supporting the idea of a spatial gradient of tactile enhancement. Overall, our findings argue for low spatial specificity of tactile enhancement at movement-relevant body parts, here the target hand.     

Color Selectivity of the Spatial Congruency Effect: Evidence from the Focused Attention Paradigm

The multisensory response enhancement (MRE), occurring when the response to a visual target integrated with a spatially congruent sound is stronger than the response to the visual target alone, is believed to be mediated by the superior colliculus (SC) (Stein & Meredith, 1993). Here, we used a focused attention paradigm to show that the spatial congruency effect occurs with red (SC-effective) but not blue (SC-ineffective) visual stimuli, when presented with spatially congruent sounds. To isolate the chromatic component of SC-ineffective targets and to demonstrate the selectivity of the spatial congruency effect we used the random luminance modulation technique (Experiment 1) and the tritanopic technique (Experiment 2). Our results indicate that the spatial congruency effect does not require the distribution of attention over different sensory modalities and provide correlational evidence that the SC mediates the effect.     

Perceptual processing of adjacent and nonadjacent tactile nontargets.

Previous research has shown that subjects appear unable to restrict processing to a single finger and ignore a stimulus presented to an adjacent finger. Furthermore, the evidence suggests that, at least for moving stimuli, an adjacent nontarget is fully processed to the level of incipient response activation. The present study replicated and expanded upon these original findings. The results of Experiment 1 showed that an equally large response-competition effect occurred when the nontarget was presented to adjacent and nonadjacent fingers (on the same hand). The results of Experiment 2 showed that the effects observed in Experiment 1 (and in previous studies) were also obtained with stationary stimuli. Although small, there was some indication in the results of Experiment 2 that interference may dissipate more rapidly with distance with stationary stimuli. An additional finding was that interference effects were observed in both experiments with temporal separations between the target and nontarget of up to 100 msec. In Experiment 3, target and nontarget stimuli were presented to opposite hands. Although reduced, interference was still evident with target and nontarget stimuli presented to opposite hands. Varying the physical distance between hands did not produce any change in the amount of interference. The results suggest that the focus of attention on the skin extends nearly undiminished across the fingers of one hand and is not dependent upon the physical distance between sites of stimulation.     

Perceptual processing of adjacent and nonadjacent tactile nontargets

Previous research has shown that subjects appear unable to restrict processing to a single finger and ignore a stimulus presented to an adjacent finger. Furthermore, the evidence suggests that, at least for moving stimuli, an adjacent nontarget is fully processed to the level of incipient response activation. The present study replicated and expanded upon these original findings. The results of Experiment 1 showed that an equally large response-competition effect occurred when the nontarget was presented to adjacent and nonadjacent fingers4on the same hand). The results of Experiment 2 showed that the effects observed in Experiment 1 (and in previous studies) were also obtained with stationary stimuli. Although small, there was some indication in the results of Experiment 2 that interference may dissipate more rapidly with distance with stationary stimuli. An additional finding was that interference effects were observed in both experiments with temporal separations between the target and nontarget of up to 100 msec. In Experiment 3, target and nontarget stimuli were presented to opposite hands. Although reduced, interference was still evident with target and nontarget stimuli presented to opposite hands. Varying the physical distance between hands did not produce any change in the amount of interference. The results suggest that the focus of attention on the skin extends nearly undiminished across the fingers of one hand and is not dependent upon the physical distance between sites of stimulation.     

Visual field x response hand interactions and level priming in the processing of laterally presented hierarchical stimuli

Hemisphere-specific processing of laterally presented global and local stimulus levels was investigated by (a) examining interactions between the visual field of stimulus presentation and the response hand and (b) comparing intra- with inter-hemispheric effects of level priming (i.e. faster and more accurate performance when the target level repeats). Although in Experiment 1, which involved two-choice responses with left and right hands, performance costs occurred when the same hemisphere received the stimulus and controlled the response hand, further analyses suggest that these effects reflect spatial compatibility rather than intra-hemispheric interference. Consistent with the spatial compatibility interpretation, in Experiment 2 a similar visual field x response interaction was obtained with regard to left and right responses given with the same hand. Trial-to-trial level priming occurred in both experiments and was unaffected by the intra-hemispheric sequence of target levels. Implications regarding hemispheric processing mode are discussed.     

Prism adaptation in alternately exposed hands

We assessed intermanual transfer of the proprioceptive realignment aftereffects of prism adaptation in right-handers by examining alternate target pointing with the two hands for 40 successive trials, 20 with each hand. Adaptation for the right hand was not different as a function of exposure sequence order or postexposure test order, in contrast with adaptation for the left hand. Adaptation was greater for the left hand when the right hand started the alternate pointing than when the sequence of target-pointing movements started with the left hand. Also, the largest left-hand adaptation appeared when that hand was tested first after exposure. Terminal error during exposure varied in cycles for the two hands, converging on zero when the right hand led, but no difference appeared between the two hands when the left hand led. These results suggest that transfer of proprioceptive realignment occurs from the right to the left hand during both exposure and postexposure testing. Such transfer reflects the process of maintaining spatial alignment between the two hands. Normally, the left hand appears to be calibrated with the right-hand spatial map, and when the two hands are misaligned, the left-hand spatial map is realigned with the right-hand spatial map.