Anatomical limitations in mental transformations of body parts

Two experiments investigated whether possible and impossible body postures influence mental rotation processes differently considering that anatomical limitations constrain the way in which subjects perform mental transformations of body parts. In Experiment 1, mental rotation was performed on two stimuli presented simultaneously. Both possible and impossible body postures elicited mental rotation, although the mental rotation rate was slower for impossible postures. In Experiment 2, only one stimulus was presented at a time and subjects decided whether it represented a correct body-part configuration or not. A typical mental rotation function was only present for correct body-part configurations. The results are discussed in terms of the familiarity of the stimuli. Unfamiliar stimuli (physically impossible) are rotated via local representations of their parts, whilst global representations are used for rotating familiar (anatomically correct) stimuli.     

Covariation of sex differences in mental rotation with body size

Sex difference in mental rotation ability was reconsidered. The Vandenberg-Kuse figures were administered to 120 male and 76 female students from the Medical School of BlackSea Technical University in Trabzon, Turkey to assess the mental rotation ability. Students' height and weight were measured. As expected, men outperformed women on this test and had greater height and weight. Number correct on mental rotation test significantly correlated with height and weight for the total sample and for men, but only with weight for women. Using weight as covariate, the sex difference was no longer significant. The mean mental rotation score was significantly higher for heavy women than for light men. There was a positive correlation between weight and mental rotation test scores for heavy women, but height and weight were negatively correlated with mental rotation test scores for light men. These results suggest that there is no sex difference in mental rotation ability as measured.     

Recognition and mental manipulation of body parts dissociate in locked-in syndrome

Several lines of evidence demonstrate that the motor system is involved in motor simulation of actions, but some uncertainty exists about the consequences of lesions of descending motor pathways on mental imagery tasks. Moreover, recent findings suggest that the motor system could also have a role in recognition of body parts. To address these issues in the present study we assessed patients with a complete damage of descending motor pathways (locked-in syndrome, LIS) on the hand laterality task, requiring subjects to decide whether a hand stimulus in a given spatial orientation represents a left or a right hand. LIS patients were less accurate than healthy controls in judging hand laterality; more importantly, LIS patients’ performance was modulated by spatial orientation of hand stimuli whereas it was not affected by biomechanical constraints. These findings demonstrate a dissociation between spared hand recognition and impaired access to action simulation processes in LIS patients.     

Representation of anatomical constraints in motor imagery: mental rotation of a body segment

Classically, the mental rotation paradigm has shown that when subjects are asked to judge whether objects that differ in orientation are spatially congruent, reaction times increase with angular discrepancy, although some reports have shown that this is not always the case. Would similar results be obtained with realistic figures of body segments? In this work, the mental rotation of a hand attached to its forearm and arm in anatomically possible and impossible starting positions is compared with the mental rotation of a hammer. The main results show that reaction times increase monotonically with the angle of discrepancy for both stimuli and that the speed of rotation is higher for anatomically possible orientations in the case of the hand. Thus, mental rotation of body segments follows the same empirical rules as objects of another nature, and biomechanical constraints imposed to the motility of these segments can be considered as attributes of the mental representation.     

Embodied spatial transformations: "body analogy" for the mental rotation of objects

The cognitive advantage of imagined spatial transformations of the human body over that of more unfamiliar objects (e.g., Shepard-Metzler [S-M] cubes) is an issue for validating motor theories of visual perception. In 6 experiments, the authors show that providing S-M cubes with body characteristics (e.g., by adding a head to S-M cubes to evoke a posture) facilitates the mapping of the cognitive coordinate system of one's body onto the abstract shape. In turn, this spatial embodiment improves object shape matching. Thanks to the increased cohesiveness of human posture in people's body schema, imagined transformations of the body operate in a less piecemeal fashion as compared with objects (S-M cubes or swing-arm desk lamps) under a similar spatial configuration, provided that the pose can be embodied. If the pose cannot be emulated (covert imitation) by the sensorimotor system, the facilitation due to motoric embodiment will also be disrupted.     

Trunk posture affects upper extremity function of adults

This study examined the effects of various seated trunk postures on upper extremity function. 59 adults were tested using the Jebsen Taylor Hand Function Test while in three different trunk postures. Significant mean differences between the neutral versus the flexed and laterally flexed trunk postures were noted during selected tasks. Specifically, dominant hand performance during the tasks of feeding and lifting heavy cans was significantly slower while the trunk was flexed and laterally flexed than when performed in the neutral trunk position. Performance of the nondomi nant hand during the tasks of picking up small objects, page turning, as well as the total score was slower while the trunk was flexed compared to performance in the neutral trunk position. These findings support the assumption that neutral trunk posture improves upper extremity performance during daily activities although the effect is not consistent across tasks. Findings are discussed along with limitations and recommendations for research.     

A parallel-process model of mental rotation

It is argued that some of the phenomena identified with analog processes by Shepard can be understood as resulting from a parallel-process algorithm running on a processor having many individual processing elements and a restricted communication structure. In particular, an algorithm has been developed and implemented which models human behavior on Shepard's object rotation and comparison task. The algorithm exhibits computation times which increase linearly with the angle of rotation. Shepard found a similar linear function in his experiments with human subjects. In addition, the intermediate states of the computation are such that if the rotation process were to be interrupted at any point, the object representation would correspond to that of the actual object at a position along the rotation trajectory. The computational model presented here is governed by three constraining assumptions: (a) that it be parallel: (b) that the communication between processors be restricted to immediate neighbors: (c) that the object representation be distributed across a large fraction of the available processors. A method of diagnosing the correct axis of rotation is also presented.     

Selective effects of motor expertise in mental body rotation tasks: comparing object-based and perspective transformations

Brain imaging studies provide strong evidence for the involvement of the human mirror system during the observation of complex movements, depending on the individual's motor expertise. Here, we ask the question whether motor expertise not only affects perception while observing movements, but also benefits perception while solving mental rotation tasks. Specifically, motor expertise should only influence the performance in mental body rotation tasks (MBRT) with left-right judgment, evoking a perspective transformation, whereas motor expertise should not affect the MBRT with same-different judgment, evoking an object-related transformation. Participants with and without motor expertise for rotational movements were tested in these two conditions in the MBRT. Results showed that motor experience selectively affected performance in the MBRT with the left-right judgment, but not with same-different judgment. More precisely, motor expertise only benefited performance when human figures were presented in (for non-experts) unfamiliar, upside-down body orientations.     

Hemisphere differences for components of mental rotation

The hemispheric functional lateralization of components of mental rotation performance was investigated. Twenty right-handed males were presented with rotated alphanumerics and unfamiliar characters in the left or right visual field. Subjects decided if the laterally presented stimulus was identical to or a mirror image of a center standard stimulus. Reaction time and errors were measured. Previous mental rotation findings were replicated and the visual field variable produced significant effects for both dependent measures. An overall right visual field advantage was observed in the latency data, suggesting a left hemisphere superiority for at least one component process of the task. A significant interaction in the error data showed that alphanumerics produced less errors in the right visual field than in the left visual field, consistent with a left hemisphere superiority for processing verbal symbolic material. No such hemispheric difference in accuracy was found for unfamiliar characters.     

Impact of practice on speed of mental rotation

We tested 11- and 20-year-olds on 3360 trials of a mental rotation task in which they judged if stimuli presented in different orientations were letters or mirror images of letters. Children's and adults' processing times decreased substantially over practice. These changes were well characterized by hyperbolic and power functions in which most of the parameters of those functions were constrained to adults' values. Performance on two transfer tasks, mental rotation of letter-like characters and memory search for numbers, indicated that the practiced skill did not generalize to other domains. The results are discussed in terms of different mechanisms that might be responsible for the impact of practice.     

A high density ERP comparison of mental rotation and mental size transformation

To compare mental rotation and mental size transformation, 128-channel EEG was recorded while subjects performed both tasks using random two-dimensional shapes as stimuli. Behavioural results showed significant linear effects of both size transformation and mental rotation on reaction times. Rotation ERPs showed experimental effects at two latencies: a bilateral component distributed over posterior parietal electrodes at a latency of approximately 232-300ms and a second component at approximately 424-492ms distributed over right anterior parietal electrodes. The latency and spatial distribution of this second effect is consistent with previous research indicating a functional connection between this component and mental rotation. ERPs for the size-transformation task showed an effect at 180-228ms distributed bilaterally over occipital-temporal electrodes. These results are consistent with previous hemodynamic imaging studies that show involvement of parietal cortex in mental rotation and also the involvement of BA 19 in size-transformation tasks. However, the superior temporal resolution of the present data indicates that BA 19 activation may occur at a latency that is more likely related to apparent motion than to the size-transformation operation per se.     

Development of mental rotation: A speed-accuracy study

Pairs of letters and numbers were shown to 11-, 14-, and 19-year-olds. One stimulus in a pair was presented upright. The second, which was either identical to the first or a mirror image of it, was rotated 0 to 150° from the vertical. Individuals judged if the stimuli in a pair would be identical or mirror images if presented at the same orientation. They did so under instructions that emphasized accurate responses, fast responses, or fast and accurate responses. Typically, responses were (1) most accurate and slowest when accuracy was emphasized, and (2) least accurate but fastest when speed was emphasized. The data from the three instructional conditions were used to derive measures of response times in which accuracy of response was equated for the three age groups. At 95% accuracy 14- and 19-year-olds mentally rotated stimuli at the same rate, which was faster than 11-year-olds' rate. At 100% accuracy, 19-year-olds mentally rotated stimuli more rapidly than both 11- and 14-year-olds, who did not differ from one another.     

The effect of body posture on long-range time-to-contact estimation

On Earth, gravity accelerates freely moving objects downward, whereas upward-moving objects are being decelerated. Do humans take internalised knowledge of gravity into account when estimating time-to-contact (TTC, the time remaining before the moving object reaches the observer)? To answer this question, we created a motion-prediction task in which participants saw the initial part of an object's trajectory moving on a collision course prior to an occlusion. Observers had to judge when the object would make contact with them. The visual scene was presented with a head-mounted display. Participants lay either supine (looking up) or prone (looking down), suggestive of the ball either rising up or falling down toward them. Results showed that body posture had a significant effect on time-to-contact estimation, but only when occlusion times were long (2.5 s). The effect was also rather small. This lack of immediacy in the posture effect suggests that TTC estimation is initially robust toward the effect of gravity, which comes to bear only as more time is allowed for post-processing of the visual information.     

Visual mental rotation of possible and impossible objects

Participants were tested on two visual mental rotation tasks using three-dimensional "possible" and "impossible" shapes. Both types of stimuli can be easily encoded by their parts and how they are spatially organized. However, while possible shapes can also be easily encoded as a global image, it is more difficult to encode impossible shapes in such a way. Participants visually rotated both types of stimuli at comparable rates, reflecting that local representations were used in the process of visual mental rotation.     

The effect of apparent movement on mental rotation

Eleven subjects were timed as they judged whether a small bar perpendicular to one side of a clockhand would point left or right if the hand was pointing upward (i.e., at the "12 o'clock" position). The clockhand was shown in two successive orientations 30 degrees apart, so that it was perceived to jump from one to the other in either a clockwise or a counterclockwise direction. Reaction times were consistent with the interpretation that the subjects "mentally rotated" the clockhand from its perceived orientation back to the upright before making their decisions. The direction of the jump influenced perceived orientation but did not influence either the direction or rate of mental rotation itself.     

Implicit transfer of motor strategies in mental rotation

Recent research indicates that motor areas are activated in some types of mental rotation. Many of these studies have required participants to perform egocentric transformations of body parts or whole bodies; however, motor activation also has been found with nonbody objects when participants explicitly relate the objects to their hands. The current study used positron emission tomography (PET) to examine whether such egocentric motor strategies can be transferred implicitly from one type of mental rotation to another. Two groups of participants were tested. In the Hand-Object group, participants performed imaginal rotations of pictures of hands; following this, they then made similar judgments of pictures of Shepard-Metzler objects. The Object-Object group performed the rotation task for two sets of Shepard-Metzler objects only. When the second condition in each group (which always required rotating Shepard-Metzler objects) was compared, motor areas (Area 6 and M1) were found to be activated only in the Hand-Object group. These findings suggest that motor strategies can be covertly transferred to imaginal transformations of nonbody objects.     

Demonstration of a mental analog of an external rotation

Subjects imagined a designated two-dimensional shape rotating within a blank, circular field at a self-determined rate. At some point during the mental rotation, a test shape was presented at one of 12 picture-plane orientations, and the subject was required to determine as rapidly as possible whether the test shape was the same as the originally designated shape or was its mirror image. When the test shape was presented in the expected orientation (the orientation assumed to correspond to the current orientation of the rotating internal representation), reaction time was short and constant, regardless of the angular departure of that orientation from a previously trained position. This was true even when the test shape was presented in an orientation which had not previously been tested. When the test shape was presented at some other, unexpected orientation, reaction time increased linearly with the angular difference between the expected orientation and the orientation of the test shape. It is argued that these results provide a demonstration of the \ldanalog\rd nature of mental rotation.     

Passive tactile feedback facilitates mental rotation of handheld objects

Mental rotation of objects improves when passive tactile information for the rotating object accompanies the imagined rotation (Wraga, Creem, & Proffitt, 2000). We examined this phenomenon further using a within-subjects paradigm involving handheld objects. In Experiment 1, participants imagined rotating an unseen object placed on their upturned palms. The participants were faster at mental rotation when the object was rotated on their palm than when the object remained stationary. Experiment 2 tested whether the performance advantage would endure when the participants received tactile information for only the start- and endpoints of the rotation event. This manipulation did not improve performance, relative to a stationary control. Experiment 3 revealed that ambiguous tactile information, continuous with the rotation event but independent of object shape, actually degraded performance, relative to a stationary control. In Experiment 4, we found that continuous tactile rotation discrepant from imagined object movement also hindered performance, as compared with continuous tactile information aligned with imagined object movement. The findings suggest a tight coupling between tactile information specifying continuous object rotation and the corresponding internal representation of the rotating object.     

The effect of landmark features on mental rotation times

By varying what we take to be the saliency oflandmarks (which are cues to location and orientation that are unique and visible from a distance), the slopes and intercepts of the time/angle function in the "mental rotation" task were caused to vary accordingly.