Sex differences in parietal lobe morphology: relationship to mental rotation performance

Structural magnetic resonance imaging (MRI) studies of the human brain have reported evidence for sexual dimorphism. In addition to sex differences in overall cerebral volume, differences in the proportion of gray matter (GM) to white matter (WM) volume have been observed, particularly in the parietal lobe. To our knowledge there have been no studies examining the relationship between the sex differences in parietal lobe structure and function. The parietal lobe is thought to be involved in spatial ability, and particularly involved in mental rotation. The purpose of this study is to examine whether sex differences in parietal lobe structure are present, and if present to relate these differences to performance on the mental rotations test (MRT). We found that women had proportionately greater gray matter volume in the parietal lobe compared to men, and this morphologic difference was disadvantageous for women in terms of performance on the MRT. In contrast, we found that men compared to women had proportionately greater parietal lobe surface area, and this morphologic difference was associated with a performance advantage for men on mental rotation. These findings support the possibility that the sexual dimorphism in the structure of the parietal lobe is a neurobiological substrate for the sex difference in performance on the mental rotations test.     

Eye-hand interactions differ in the human premotor and parietal cortices

In order to successfully look at and reach for a visual target the central nervous system must perform a complex sensorimotor transformation. How this transformation is mapped onto relevant brain structures has become the subject of much recent investigation. In the present paper we examined the contribution of the human premotor cortex (PMC) to this transformation process during a task requiring coordinated eye and hand movements. For this purpose, we made use of single-pulse transcranial magnetic stimulation (TMS) to temporarily disrupt the processing occurring in the PMC during task performance. Subjects made open-loop pointing movements accompanied by saccades of the same size or two or three times larger. Under normal circumstances without TMS, the pointing movement amplitude increased with saccade amplitude. When TMS was applied over the PMC 100-200 ms after target presentation, the influence of saccade amplitude on the pointing movement amplitude was increased. This is the opposite effect to that observed in a previous study [Journal of Neurophysiology 84 (200) 1677-1680] when TMS was applied over the posterior parietal cortex (PPC) during the same task. We suggest that this pattern of results is consistent with the coding of the reach plan in eye-centered coordinates in the PPC and limb-centered coordinates in the PMC.     

Children's left parietal brain activation during mental rotation is reliable as well as specific

Some recent evidence suggests that mental rotation of characters in children aged 7 or 8 years might be lateralized to the left parietal hemisphere. An alternative statement exists, however, the finding might be completely unspecific for mental rotation but either be simply a function of task difficulty or a consequence of the use of characters as stimuli. To test these alternatives, ERPs of 24 second graders were measured twice: (a) during mental rotation with characters as stimuli and orientations of 30°, 90°, or 150° and (b) during memory scanning with characters as stimuli and set sizes of 1, 2, or 3 letters. In both cases, an amplitude modulation was found. The effect of mental rotation as a function of character orientation turned out to be lateralized to the left parietal hemisphere. The effect of memory scanning as a function of set size, however, turned out to be completely non-lateralized. Thus, children's left hemisphere activation during mental rotation is reliable as well as specific.     

Differential roles of the frontal and parietal cortices in the control of saccades

Although externally as well as internally-guided eye movements allow us to flexibly explore the visual environment, their differential neural mechanisms remain elusive. A better understanding of these neural mechanisms will help us to understand the control of action and to elucidate the nature of cognitive deficits in certain psychiatric populations (e.g. schizophrenia) that show increased latencies in volitional but not visually-guided saccades. Both the superior precentral sulcus (sPCS) and the intraparietal sulcus (IPS) are implicated in the control of eye movements. However, it remains unknown what differential contributions the two areas make to the programming of visually-guided and internally-guided saccades. In this study we tested the hypotheses that sPCS and IPS distinctly encode internally-guided saccades and visually-guided saccades. We scanned subjects with fMRI while they generated visually-guided and internally-guided delayed saccades. We used multi-voxel pattern analysis to test whether patterns of cue related, preparatory and saccade related activation could be used to predict the direction of the planned eye movement. Results indicate that patterns in the human sPCS predicted internally-guided saccades but not visually-guided saccades in all trial periods and patterns in the IPS predicted internally-guided saccades and visually-guided saccades equally well. The results support the hypothesis that the human sPCS and IPS make distinct contributions to the control of volitional eye movements.     

Manual training of mental rotation

The aim of this study was to investigate the timing relations between phonological encoding that is, the generation of an abstract phonological representation of a to-be-produced utterance and the initiation of articulation. Previous research (Meyer &; Schriefers, 1991) using a picture-word paradigm suggested that, in the production of simple one-word naming responses, a speaker completes phonological encoding of the complete word before articulation is initiated. In the present study, this question was investigated for the production of German no-determiner noun phrases (e.g. roter Tisch, “red table”;). The results showed reliable facilitation effects for distractors that are identical to the first syllable of the first word of the noun phrase. For the second syllable of the first word, only weak facilitation effects were obtained. For the second word, no significant facilitation effects were obtained. However, additional analyses showed that two groups of speakers can be distinguished, one showing only facilitation effects for the first syllable of the first word, and the other showing an additional facilitation effect for the second syllable of the first word. Together with related results, our findings lead to two conclusions. First, the (phonological) word is not the lower limit of phonological encoding before articulation can be initiated. Second, speakers can adjust the size of the advance planning unit at the phonological level based on the specific speaking context.     

Fear and anxiety modulate mental rotation

We used an emotional priming paradigm to investigate whether fear and anxiety modulate mental rotation of abstract three-dimensional objects (i.e., Shepard-Metzler figures). On each trial, participants viewed pairs of objects and decided whether the objects had the identical shape by mentally rotating the one on the right into congruence with the one on the left. The participants viewed a picture of a face—fearful or neutral—briefly before the pairs of objects appeared. Participants with high state anxiety, and not those with low state anxiety, rotated the objects more quickly after they saw fearful faces than after they saw neutral faces. This result not only documents that fear can improve mental rotation but also shows that this effect is modulated by the emotional arousal of the participants.     

Applications of mental rotation figures of the Shepard and Metzler type and description of a mental rotation stimulus library

The 3D cube figures used by Shepard and Metzler [Shepard, R. N., & Metzler, J. (1971). Mental rotation of three-dimensional objects. Science, 171, 701-703] have been applied in a broad range of studies on mental rotation. This note provides a brief background on these figures, their general use in cognitive psychology and their role in studying spatial behavior. In particular, it is pointed out that large sex differences with the 3D mental rotation figures tend to be observed only in particular tasks, such as the Vandenberg and Kuse test [Vandenberg, S. G., & Kuse, A. R. (1978). Mental rotations, a group test of three-dimensional spatial visualization. Perceptual and Motor Skills, 47, 599-604] that involve multiple figures within a single problem. In contrast, pairwise presentation of the same 3D figures yields either small or no significant sex differences. In the context of the very broad range of ongoing research done with 3D figures, and the desirability of uniformity in the stimulus material used, we introduce a library of 16 cube mental rotation figures, each presented in orientations ranging from 0 to 360 degr in 5 degr steps, and with its mirror image, for a total of 2336 figures. This library, freely available to researchers, will help in the creation of mental rotation tasks both for presentation on the computer screen and for pencil and paper applications.     

Reference frames in mental rotation

Four experiments are reported that investigate whether images or reference frames are transformed during a mental rotation task. In all experiments a display of four identical letters (P1) was presented at either +90 degrees or -90 degrees from upright, and subjects had to decide whether the letters were normal or mirror-image reflections. A single letter (P2) was then presented 100 ms later in a variable orientation with the same task instructions. Reaction times to P2 were assessed to determine whether an image of P2 was rotated to upright or whether an internal reference frame was rotated into congruence with P2 from the orientation of P1. The results as a whole suggest that transformations of P2 can be initiated either relative to upright or relative to the orientation of P1. They further indicate that the probability of using each reference orientation can be changed by procedural variations. The findings are most parsimoniously interpreted as suggesting that mental rotation involves the transformation of reference frames rather than the transformation of template-like representations.     

Developmental changes in mental rotation

Subjects from Grades 3, 4, 6, and college judged whether pairs of stimuli were identical or mirror-image reversals. One stimulus of a pair was presented upright; the other was rotated 0 to 150° from the standard. The pairs were either alphanumeric symbols or unfamiliar, letter-like characters of the type found on the PMA Spatial Ability Test. Response latencies were measured. The primary results were that (a) the speed of mental rotation increased with development, (b) unfamiliar characters were rotated more slowly than alphanumeric characters, by approximately the same amount at each grade, and (c) unfamiliar characters were encoded and compared more slowly than alphanumeric symbols, by an amount that declined with development. The results are discussed in terms of the component processes that underlie developmental change and individual variation in mental rotation skill.     

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.     

Controlled and automatic processing during mental rotation

In two experiments, 9- and 10-year-olds and adults were tested on a mental rotation task in which they judged whether stimuli presented in different orientations were letters or mirror-images of letters. The mental rotation task was performed alone on 48 trials and concurrently with a memory task on 48 additional trials. The concurrent memory task in Experiment 1 was recalling digits; in Experiment 2, recalling positions in a matrix. The key result was that the slope of the function relating response time to stimulus orientation was the same when the mental rotation task was performed alone and when performed concurrently with the memory task. This result is interpreted as showing that mental rotation is an automatic process for both children and adults.     

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.     

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.     

Behavioral, but not reward, risk modulates activation of prefrontal, parietal, and insular cortices

Risky decisions may involve uncertainty about possible outcomes (i.e., reward risk) or uncertainty about which action should be taken (i.e., behavioral risk). Determining whether different forms of risk have distinct neural correlates is a central goal of neuroeconomic research. In two functional magnetic resonance imaging experiments, subjects viewed shapes that had well-learned response-reward contingencies. Magnitude of a monetary reward was held constant within one experiment, whereas expected value was held constant within the other. Response selection, in the absence of behavioral risk, evoked activation within a broad set of brain regions, as had been found in prior studies. However, behavioral risk additionally modulated activation in prefrontal, parietal, and insular regions, within which no effect of reward risk was observed. Reward delivery, in comparison with omission, evoked increased activity in the ventromedial prefrontal cortex and the nucleus accumbens. We conclude that distinct brain systems are recruited for the resolution of different forms of risk.     

Sex differences in mental rotation strategy

When humans decide whether two visual stimuli are identical or mirror images of each other and one of the stimuli is rotated with respect to the other, the time discrimination takes usually increases as a rectilinear function of the orientation disparity. On the average, males perform this mental rotation at a faster angular speed than females. This experiment required the rotation of both mirror-image-different and non-mirror-different stimuli. The polygonal stimuli were presented in either spatially unfiltered, high-pass or low-pass filtered versions. All stimulus conditions produced mental rotation-type effects but with graded curvilinear trends. Women rotated faster than men under all conditions, an infrequent outcome in mental rotation studies. Overall, women yielded more convexly curvilinear response functions than men. For both sexes the curvilinearity was more pronounced under the non-mirror-different, low-pass stimulus condition than under the mirror different, high-pass stimulus condition. The results are considered as supporting the occurrence of two different mental rotation strategies and as suggesting that the women were predisposed to use efficiently an analytic feature rotation strategy, while the men were predisposed to employ efficiently a holistic pattern rotation strategy. It is argued that the overall design of this experiment promoted the application of an analytic strategy and thus conferred an advantage to the female participants.     

Improved mental rotation by near-sighted subjects

Several studies have shown significant correlations among factors such as sex, age, and hormone levels with performance on mental rotation tasks. To perform spatial rotation also seems to be related to cognitive abilities such as musical skills. The present experiment investigated a possible relationship for enhanced spatial abilities, as observed in near-sighted subjects, with mental rotation performance. 39 near-sighted and 21 normal-sighted subjects were tested on a mental rotation task using two-dimensional representations of three-dimensional objects. Near-sighted subjects displayed fewer errors in possible rotations than normal-sighted subjects. There was no difference in errors between groups in identification of mirror images ("impossible rotations"). Results were interpreted in terms of a relation between enhanced reliance on nonvisual information by near-sighted subjects and improved spatial representation.     

Developmental differences in mental rotation.

A reaction time paradigm was used to investigate developmental differences in ability to rotate and compare imaginal representations. Third grade, fifth grade, and college students (ages 9, 11, and 20 years, respectively) were required to determine whether a letter of the alphabet was presented in its backward or normal position. Letters were presented at 0, 60, 120, 180, 240, or 300° orientations from upright. Subjects were given no advance information about a test letter, or they were given identity and orientation information. In the no information condition, reaction time increased for all age groups as a function of the departure in orientation of the test letter from an upright position. In the advance information condition, reaction time remained uniform across orientation for only the college subjects. The developmental implications of these findings are discussed.     

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.     

The relationship between mental rotation and representational momentum

Two experiments explored a possible relationship between mental rotation and representational momentum, a task in which participants were asked to remember an object's position following a sequence of images implying motion. Typically, participants misremember the position as distorted forward along the implied trajectory. If representational momentum relies on mental imagery, the magnitude of memory distortion in a representational momentum task should be positively correlated with the rate of mental rotation. As predicted, faster mental rotation rates and larger memory distortions for object position were observed for rotational axes aligned with the viewers' coordinate system. In addition, participants with slower mental rotation rates produced smaller memory distortions in the implied-event task.