Symmetry in haptic and in visual shape perception

Four experiments tested the hypothesis that bilateral symmetry is an incidental encoding property in vision, but can also be elicited as an incidental effect in touch, provided that sufficient spatial reference information is available initially for haptic inputs to be organized spatially. Experiment 1 showed that symmetry facilitated processing in vision, even though the task required judgments of stimulus closure rather than the detection of symmetry. The same task and stimuli failed to show symmetry effects in tactual scanning by one finger (Experiment 2). Experiment 3 found facilitating effects for vertically symmetric open stimuli, although not for closed patterns, in two-forefinger exploration when the fore-fingers had previously been aligned to the body midaxis to provide body-centered spatial reference. The one-finger exploration condition again failed to show symmetry effects. Experiment 4 replicated the facilitating effects of symmetry for open symmetric shapes in tactual exploration by the two (previously aligned) forefingers. Closed shapes again showed no effect. Spatial-reference information, finger movements, and stimulus factors in shape perception by touch are discussed.     

Center of mass perception and inertial frames of reference

Center of mass perception was investigated by varying the shape, size, and orientation of planar objects. Shape was manipulated to investigate symmetries as information. The number of reflective symmetry axes, the amount of rotational symmetry, and the presence of radial symmetry were varied. Orientation affected systematic errors. Judgments tended to undershoot the center of mass. Random errors increased with size and decreased with symmetry. Size had no effect on random errors for maximally symmetric objects, although orientation did. The spatial distributions of judgments were elliptical. Distribution axes were found to align with the principle moments of inertia. Major axes tended to align with gravity in maximally symmetric objects. A functional and physical account was given in terms of the repercussions of error. Overall, judgments were very accurate.     

The preference for symmetry in flower-naïve and not-so-naïve bumblebees

Truly flower-naïve bumblebees, with no prior rewarded experience for visits on any visual patterns outside the colony, were tested for their choice of bilaterally symmetric over asymmetric patterns in a radial-arm maze. No preference for symmetry was found. Prior training with rewarded black and white disks did, however, lead to a significant preference for symmetry. The preference was not specific to symmetry along the vertical axis: a preference for horizontal symmetry was found as well. The results challenge the notion that a preference for bilateral symmetry is unlearned. The preference for symmetry was the product of non-differential conditioning.     

Encoding and Maintaining Reference in Oral Discourse

This study deals with information management and reference encoding modes in oral discourse production. Three potentially influential factors were the distance between the first occurrence of an item and its later occurrences, a topic change that takes the focus off that item, and the span of the conceptual information available for verbalization. French-speaking adult subjects were asked to tell stories from comic strips to a listener who was unfamiliar with them. The frames in each strip were presented simultaneously or in succession. Four versions were generated for each comic strip: a given version was either short (three frames) or long (eight frames), and either did or did not have a topic change. The results showed that the target character was usually marked as a given, regardless of the version. This was more often true, however, when the topic did not change. When the character was treated as a given, referent accessibility marking was dependent on (1) topic change alone when the frames were presented simultaneously, and (2) topic change and comic strip length when the frames were presented in succession. The discussion analyzes the results in terms of the allocation of cognitive resources to maintaining coreference and to assisting addressees in their processing.     

Symmetry, gestalt and information theory

Two kinds of patterns were made up out of crosses. The first kind was symmetrical and the second contained a sub-pattern repeated in the same orientation. Subjects were requested to reproduce the stimuli after viewing them for 2 sec. It was found that there was no difference between the two kinds of stimuli when symmetry about the horizontal axis was involved but that when symmetry about the vertical axis occurred the symmetrical stimuli were reproduced more accurately than the repeated stimuli. Introduction of contrasting colours on the two portions of each pattern decreased the frequency of correct responses, whilst stressing the grid line subdividing the stimuli into two portions containing the same information had no significant effect.     

Regularity of symmetry verticality guides perceptual judgments of objects

Previous research indicated that most salient, real-world objects possess natural regularities that observers commonly assume in perceptual judgments of figural orientation and interpretation. Regularities include 3-dimensionality, bilateral symmetry, and the tendency for object tops to possess more salient information than bottoms. Thus, when observers interpret randomly shaped figures, they reliably impose volume, bilateral symmetry, and top and front orientation directions, even when figures are 2-dimensional and asymmetric. We confirmed generalizability for observers to assume these regularities with stimuli that vary in complexity, and we found evidence supporting another regularity, that of symmetry verticality (symmetry about a vertical axis). Findings support use of a family of perceptual heuristics corresponding to natural regularities that constrain stimulus indeterminacy and help guide judgment of object orientation and interpretation.     

Symmetry perception in the blind

Bilateral mirror symmetry, especially vertical symmetry, is a powerful phenomenon in spatial organization of visual shapes. However, the causes of vertical symmetry salience in visual perception are not completely clear. Here we investigated whether the perceptual salience of vertical symmetry depends on visual experience by testing a group of congenitally blind individuals in a memory task in which either horizontal or vertical symmetry was used as an incidental feature. Both blind and sighted subjects remembered more accurately configurations that were symmetrical compared to those that were not. Critically, whereas sighted subjects displayed a higher level of facilitation by vertical than horizontal symmetry, no such difference was found in the blind. This suggests that the perceptual salience of the vertical dimension is visually based.     

Haptic perception in newborns

Two experiments using different procedures were performed in which newborns’ ability to process information about object shape with their hands was explored. In the first experiment, a haptic fixed‐trial procedure was used and a decrease in holding times was found for both right and left hands. In the second experiment, discrimination between objects was studied in which a shifted procedure associated to an infant‐control procedure followed by a dishabituation procedure was used. Habituation to an object and a reaction to the novelty of a new object were shown for both right and left hands, showing that neonates are able to process and encode some information about object shape and then to discriminate between different shapes. It is the first evidence of such an ability in neonates. Methodological procedure and haptic cognition with regard to sensory symmetry are discussed and some developmental perspectives are proposed.     

Center of mass perception: Perturbation of symmetry

Bingham and Muchisky (1993) found that observers were very accurate in determining the location of the center of mass in planar objects. Systematic errors were affected primarily by object orientation, while random errors varied with the amount of symmetry. Radial and axial reflective symmetry affected errors in different ways. In the current study, we investigated the different effects of axial reflective versus rotational symmetry. All random errors decreased with increasing rotational symmetry. Axial reflective symmetry further reduced errors in the direction perpendicular to the axis. We replicated the effect on systematic error of orientation. However, we also found an effect of the perturbation of symmetry that suggested that observers used an approximation to symmetry. To investigate this possibility, we constructed a series of objects in which axial reflective symmetry was established and then perturbed by varying amounts. We found that systematic errors were structured by the underlying approximate symmetries, and we discuss the problem of quantifying symmetry.     

Effects of partial symmetry, exposure time, and backward masking on judged goodness and reproduction of visual patterns

Six experiments investigated the effects of partial symmetry in visual patterns on judgement of pattern goodness, immediate memory, and learning. In Experiments 1—III pattern goodness ratings were substantially inter-correlated among a self-paced test condition and two conditions producing moderate to severe stimulus degradation (brief tachistoscopic exposure, and backward masking): the less the partial symmetry in a pattern, the lower was the judged goodness of the pattern. In Experiments IV and V immediate reproduction of patterns was observed respectively following exposures of 5-5000 ms, and backward masking. Correct reproduction improved with degree of partial symmetry. Concordant results were found in a free recall learning task (Experiment VI). Correlations between goodness and learning and memory performance for discrete patterns were always substantial. The results strongly suggest that pattern goodness can be appraised reliably and accurately with information processing times too short to permit pattern encoding in short-term visual memory. Evaluation of pattern goodness must therefore rest upon early (precategorical) processing of symmetry features.     

Mid-level feature contributions to category-specific gaze guidance

Our research has previously shown that scene categories can be predicted from observers’ eye movements when they view photographs of real-world scenes. The time course of category predictions reveals the differential influences of bottom-up and top-down information. Here we used these known differences to determine to what extent image features at different representational levels contribute toward guiding gaze in a category-specific manner. Participants viewed grayscale photographs and line drawings of real-world scenes while their gaze was tracked. Scene categories could be predicted from fixation density at all times over a 2-s time course in both photographs and line drawings. We replicated the shape of the prediction curve found previously, with an initial steep decrease in prediction accuracy from 300 to 500 ms, representing the contribution of bottom-up information, followed by a steady increase, representing top-down knowledge of category-specific information. We then computed the low-level features (luminance contrasts and orientation statistics), mid-level features (local symmetry and contour junctions), and Deep Gaze II output from the images, and used that information as a reference in our category predictions in order to assess their respective contributions to category-specific guidance of gaze. We observed that, as expected, low-level salience contributes mostly to the initial bottom-up peak of gaze guidance. Conversely, the mid-level features that describe scene structure (i.e., local symmetry and junctions) split their contributions between bottom-up and top-down attentional guidance, with symmetry contributing to both bottom-up and top-down guidance, while junctions play a more prominent role in the top-down guidance of gaze.     

Appearance of symmetry, beauty, and health in human faces

Symmetry is an important concept in biology, being related to mate selection strategies, health, and survival of species. In human faces, the relevance of left-right symmetry to attractiveness and health is not well understood. We compared the appearance of facial attractiveness, health, and symmetry in three separate experiments. Participants inspected front views of faces on the computer screen and judged them on a 5-point scale according to their attractiveness in Experiment 1, health in Experiment 2, and symmetry in Experiment 3. We found that symmetry and attractiveness were not strongly related in faces of women or men while health and symmetry were related. There was a significant difference between attractiveness and symmetry judgments but not between health and symmetry judgments. Moreover, there was a significant difference between attractiveness and health. Facial symmetry may be critical for the appearance of health but it does not seem to be critical for the appearance of attractiveness, not surprisingly perhaps because human faces together with the human brain have been shaped by adaptive evolution to be naturally asymmetrical.     

Young children's processing of asymmetrical and symmetrical patterns

Dot patterns varying in type of symmetry (double symmetry, vertical symmetry, horizontal symmetry, and asymmetry) were presented tachistoscopically for 200 msec, followed by a patterned mask, to kindergarten, second-grade, and fourthgrade children. All subjects reported symmetrical patterns more accurately than asymmetrical patterns. Double symmetry patterns were reproduced more accurately than vertical symmetry patterns, and vertical symmetry patterns were reproduced more accurately than horizontal symmetry patterns. These results stand in marked contrast to previous research by demonstrating that the ability to process symmetrical relationships evolves early in perceptual development. There was a suggestion that subjects of all ages perceived information about the type of symmetry presented in the display, but there were agerelated differences in subjects' abilities to use this knowledge in constructing their responses. Additionally, analyses revealed no age-related biases toward imposing symmetrical responses on asymmetrical patterns.     

The role of the human extrastriate visual cortex in mirror symmetry discrimination: a TMS-adaptation study

The human visual system is able to efficiently extract symmetry information from the visual environment. Prior neuroimaging evidence has revealed symmetry-preferring neuronal representations in the dorsolateral extrastriate visual cortex; the objective of the present study was to investigate the necessity of these representations in symmetry discrimination. This was accomplished by the use of state-dependent transcranial magnetic stimulation, which combines the fine resolution of adaptation paradigms with the assessment of causality. Subjects were presented with adapters and targets consisting of dot configurations that could be symmetric along either the vertical or horizontal axis (or they could be non-symmetric), and they were asked to perform a symmetry discrimination task on the targets while fixating the center of the screen. TMS was applied during the delay between the adapter and the test stimulus over one of four different sites: Left or Right V1/V2, or left or right dorsolateral extrastriate cortex (DLO). TMS over both Left and Right DLO reduced the adaptation effect in detecting vertical and horizontal symmetry, although the Left DLO effect on horizontal symmetry and the Right DLO effect on both vertical and horizontal symmetry were present only when considering subjects who showed a behavioral adaptation effect in the baseline No-TMS condition. Application of TMS over the Left or Right V1/V2 did not modulate the adaptation effect. Overall, these data suggest that both the Left and Right DLO contain neuronal representations tuned to mirror symmetry which play a causal role in symmetry discrimination.     

Associative symmetry in the pigeon after successive matching-to-sample training

If an organism is explicitly taught an A→B association, then might it also spontaneously learn the symmetrical B→A association? Little evidence attests to such “associative symmetry” in nonhuman animals. We report for the first time a clear case of associative symmetry in the pigeon. Experiment 1 used a successive go/no go matching‐to‐sample procedure, which showed all of the training and testing stimuli in one location and intermixed arbitrary and identity matching trials. We found symmetrical responding that was as robust during testing (B→A) as during training (A→B). In Experiment 2, we trained different pigeons using only arbitrary matching trials before symmetry testing. No symmetrical responding was found. In Experiment 3, we trained other pigeons with only arbitrary matching trials and then tested for symmetry. When these pigeons, too, did not exhibit symmetrical responding, we retrained them with intermixed identity and arbitrary matching trials. Less robust symmetrical responding was obtained here than in Experiment 1. Collectively, these results suggest that identity matching may have to be learned concurrently with arbitrary matching from the outset of training for symmetry to emerge.     

大学生在社会困境中的公平决策:社会价值取向的影响

通过两项研究考查大学生在社会困境中的行为决策及公平感体验,检验社会价值取向的影响作用,有效被试分别为85名和84名。结果表明:(1)亲社会者比亲自我者更倾向做公平决策;信息对称比不对称条件更促进被试做公平决策;女生比男生更倾向做公平决策。(2)性别在社会价值取向与信息对称性对公平决策的影响中起调节作用,社会价值取向显著影响男生的公平决策,信息对称性显著影响女生的公平决策。(3)社会价值取向显著影响个体对不公平的容忍度,亲社会者更不容忍不公平行为。(4)对于利己的不公平行为,被试都倾向接受,亲社会者并不比亲自我者体验到更强的内疚情绪;对于不利己的不公平行为,被试都倾向拒绝,且产生较强的不公平感及气愤情绪。     

Preference for symmetry is experience dependent in newborn chicks (Gallus gallus)

Spontaneous pecking preferences toward symmetric or asymmetric stimuli were tested in newborn chicks (Gallus gallus). A preference for asymmetric patterns was found in na?ve chicks (either 24 or 48 hours old), although a preference for symmetry appeared at retest after chicks had experienced standard rearing conditions (Experiments 1 and 2). Only food-experienced chicks preferred symmetric patterns; food-deprived and hand-fed chicks did not show any preference (Experiment 3). A key factor that allowed for the emergence of a preference for symmetry may relate to the improving of pecking sensorimotor skills occurring during active food manipulation. Possible explanations are discussed for the late emergence of the preference for symmetry and for the preference for asymmetry found in na?ve chicks.     

The role of visible persistence for perception of visual bilateral symmetry1

Abstract: Although the detection of visual bilateral symmetry has been claimed to be highly efficient, the possible involvement and function of visual memory in such efficient mechanisms has rarely been examined. We hypothesized that symmetry perception is rapid, as it can be achieved from rapidly decaying information of visible persistence. To test this hypothesis, we employed a temporal integration paradigm. A symmetric dot pattern was randomly divided into two asymmetric patterns and presented successively with a blank screen presented between patterns. Observers could detect symmetry when the two patterns were presented close in time (Experiment 1), indicating that observers perceived symmetry presumably utilizing visible persistence. In addition, the inverse‐intensity effect of visible persistence (Di Lollo & Bischof, 1995) was evident in our temporal integration task of symmetry (Experiment 2). The results of the current study clearly demonstrate that the detection of symmetry can be achieved based on the visible persistence. The large capacity and high spatial precision of visible persistence might be adequate for the rapid and spatially global encoding of visual symmetry.     

Detecting symmetry and faces: Separating the tasks and identifying their interactions

Face and symmetry processing have common characteristics, and several lines of evidence suggest they interact. To characterize their relationship and possible interactions, in the present study we created a novel library of images in which symmetry and face-likeness were manipulated independently. Participants identified the target that was most symmetric among distractors of equal face-likeness (Experiment 1) and identified the target that was most face-like among distractors of equal symmetry (Experiment 2). In Experiment 1, we found that symmetry judgments improved when the stimuli were more face-like. In Experiment 2, we found a more complex interaction: Image symmetry had no effect on detecting frontally viewed faces, but worsened performance for nonfrontally viewed faces. There was no difference in performance for upright versus inverted images, suggesting that these interactions occurred on the parts-based level. In sum, when symmetry and face-likeness are independently manipulated, we find that each influences the perception of the other, but the nature of the interactions differs.     

Direction of Report in Spatial and Verbal Serial Short term Memory

Four experiments examined the role played by item and order information in determining the effects of order of report of a sequence from short-term memory. Experiments in which list items were re-presented prior to recall so that only their order had to be reported showed no differences in performance between the forward and backward direction of report. This result was found with lists of auditory-verbal, visual-verbal, and spatial stimuli. When the list items were not re-presented, so that recall of both items and order was required, recall in the backward direction of report was significantly worse than in the forward direction of report, both in spatial and verbal tasks. The results point to the symmetry of inter-item associations, though only equivocally so, but they suggest strongly that the processes of spatial and verbal serial recall share many functional characteristics.