What do you mean with “direction”? Local and global cues to biological motion perception in pigeons

AbstractBiological motion point-light displays are a rich and versatile instrument to study perceptual organization. Humans are able to retrieve information from biological motion through at least two different channels: The global articulated structure as revealed by the non-rigid, yet highly constrained deformation of the dot pattern, and the characteristics of local motion trajectories of individual dots. Here, we tested eight pigeons on a task in which they had to discriminate a left-facing from a right-facing biological motion point-light figure. Since the two stimuli were mirror-flipped versions of each other, we were not sure if the birds would be able to solve the task at all. However, all birds learned the discrimination quickly and performed at high accuracy. We then challenged them with a number of test trials introduced into the sequence of the normal training trials. Tested on backwards moving walkers, the majority of the birds indicated that they used local motion cues to solve the training task, while the remaining birds obviously used global, configural cues. Testing the pigeons on different versions of scrambled biological motion confirmed that each individual bird had made a clear decision for one of the two potentially available strategies. While we confirm a previously described local precedence in processing visual patterns, the fact that some birds used global features suggests that even the birds who relied on local cues probably dispose of the perceptual abilities to use global structure, but “chose” to not use them

Decomposing biological motion: A framework for analysis and synthesis of human gait patterns.

Biological motion contains information about the identity of an agent as well as about his or her actions, intentions, and emotions. The human visual system is highly sensitive to biological motion and capable of extracting socially relevant information from it. Here we investigate the question of how such information is encoded in biological motion patterns and how such information can be retrieved. A framework is developed that transforms biological motion into a representation allowing for analysis using linear methods from statistics and pattern recognition. Using gender classification as an example, simple classifiers are constructed and compared to psychophysical data from human observers. The analysis reveals that the dynamic part of the motion contains more information about gender than motion-mediated structural cues. The proposed framework can be used not only for analysis of biological motion but also to synthesize new motion patterns. A simple motion modeler is presented that can be used to visualize and exaggerate the differences in male and female walking patterns

The relationship between social anxiety and the perception of depth-ambiguous biological motion stimuli is mediated by inhibitory ability

Orthographically projected biological motion stimuli are depth-ambiguous. Consequently, their projection when oriented towards the viewer is the same as when oriented away. Despite this, observers tend to interpret such stimuli as facing the viewer more often. Some have speculated that this facing-the-viewer bias may exist for sociobiological reasons: Mistaking another human as retreating when they are actually approaching could have more severe consequences than the opposite error. An implication of this theory is that the facingtowards percept may be perceived as more threatening than the facing-away percept. Given this, as well as the finding that anxious individuals have been found to display an attentional bias towards threatening stimuli, we reasoned that more anxious individuals might have stronger facing-the-viewer biases. Furthermore, since anxious individuals have been found to perform poorer on inhibition tasks, we hypothesized that inhibitory ability would mediate the relationship between anxiety and the facing-the-viewer bias (i.e., difficulty inhibiting the threatening percept). Exploring individual differences, we asked participants to complete anxiety questionnaires, to perform a Go/No-Go task, and then to complete a perceptual task that allowed us to assess their facing-theviewer biases. As hypothesized, we found that both greater anxiety and weaker inhibitory ability were associated with greater facing-the-viewer biases. In addition, we found that inhibitory ability significantly mediated the relationship between anxiety and facing-the-viewer biases. Our results provide further support that the facing-theviewer bias is sensitive to the sociobiological relevance of biological motion stimuli, and that the threat bias for ambiguous visual stimuli is mediated by inhibitory ability

Does anxiety induced by social interaction influence the perception of bistable biological motion?

When observing point light walkers orthographically projected onto a frontoparallel plane, the direction in which they are walking is ambiguous. Nevertheless, observers more often perceive them as facing towards than as facing away from them. This phenomenon is known as the "facing-the-viewer bias" (FTV). Two interpretations of the facing-the-viewer bias exist in the literature: a top-down and a bottom-up interpretation. Support for the top-down interpretation comes from evidence that social anxiety correlates with the FTV bias. However, the direction of the relationship between the FTV bias and social anxiety is inconsistent across studies and evidence for a correlation has mostly been obtained with relatively small samples. Therefore, the first aim of the current study was to provide a strong test of the hypothesized relationship between social anxiety and the facing-the-viewer bias in a large sample of 200 participants recruited online. In addition, a second aim was to further extend top-down accounts by investigating if the FTV bias is also related to autistic traits. Our results replicate the FTV bias, showing that people indeed tend to perceive orthographically projected point light walkers as facing towards them. However, no correlation between the FTV bias and social interaction anxiety (tau = -0.01, p = .86, BF = 0.18) or autistic traits (tau = -0.0039, p = .45, BF = 0.18) was found. As such, our data cannot confirm the top-down interpretation of the facing-the-viewer bias

The Effect of Looming and Receding Sounds on the Perceived In-Depth Orientation of Depth-Ambiguous Biological Motion Figures

BACKGROUND: The focus in the research on biological motion perception traditionally has been restricted to the visual modality. Recent neurophysiological and behavioural evidence, however, supports the idea that actions are not represented merely visually but rather audiovisually. The goal of the present study was to test whether the perceived in-depth orientation of depth-ambiguous point-light walkers (plws) is affected by the presentation of looming or receding sounds synchronized with the footsteps. METHODOLOGY/PRINCIPAL FINDINGS: In Experiment 1 orthographic frontal/back projections of plws were presented either without sound or with sounds of which the intensity level was rising (looming), falling (receding) or stationary. Despite instructions to ignore the sounds and to only report the visually perceived in-depth orientation, plws accompanied with looming sounds were more often judged to be facing the viewer whereas plws paired with receding sounds were more often judged to be facing away from the viewer. To test whether the effects observed in Experiment 1 act at a perceptual level rather than at the decisional level, in Experiment 2 observers perceptually compared orthographic plws without sound or paired with either looming or receding sounds to plws without sound but with perspective cues making them objectively either facing towards or facing away from the viewer. Judging whether either an orthographic plw or a plw with looming (receding) perspective cues is visually most looming becomes harder (easier) when the orthographic plw is paired with looming sounds. CONCLUSIONS/SIGNIFICANCE: The present results suggest that looming and receding sounds alter the judgements of the in-depth orientation of depth-ambiguous point-light walkers. While looming sounds are demonstrated to act at a perceptual level and make plws look more looming, it remains a challenge for future research to clarify at what level in the processing hierarchy receding sounds affect how observers judge the in-depth perception of plws

Phenomenal competition for poses of the human head

Abstract. We show a cylindrical projection of the human head. This projection is ambiguous with respect to head pose. Viewing such a projection produces perceptual competition for a few discrete views. In a number of studies it is suggested that the brain may represent head pose in terms of a discrete set of preferred views. Exactly what these views are and how their representations enable visual face recognition and pose estimation is not entirely clear. On the one hand, it is easier to find neurons in the primate inferotemporal cortex that are more selective for head-on, profile, or back views than other angles (Perrett et al 1991). On the other hand, psychophysical studies have shown that human face recognition generalizes better from a learned view near 45° about the vertical axis than from other views (Bruce and Valentine 1987; Troje and BulthofF, in press). This latter observation is consistent with theoretical predictions based on virtual views for symmetric objects (Vetter et al 1993). In either case, one might expect that if an image of a human head is presented in such a way as to make pose assignment ambiguous, we might visually experience a competition for preferred poses

Correlated changes in perceptions of the gender and orientation of ambiguous biological motion figures

SummaryThe sensitivity of the mammalian visual system to biological motion cues has been shown to be general and acute [1–3]. Human observers, in particular, can deduce higher-order information, such as the orientation of a figure (which way it is facing), its gender, emotional state, and even personality traits, on the basis only of sparse motion cues. Even when the stimulus information is confined to point lights attached to the major joints of an actor (so-called point-light figures), observers can use information about the way the actor is moving to tell what they are doing, whether they are a male or female, and how they are feeling [4–6]. Here we report the novel finding that stimulus manipulations that made such walkers appear more female also had the effect of making the walkers appear more often as if they were walking away from rather than towards observers. Using frontal-view (or rear-view) point-light displays of human walkers, we asked observers to judge whether they seemed to be walking towards or away from the viewing position. Independent of their own gender, observers reliably reported those figures they perceived to be male as looking like they were approaching (as reported in [7]), but those they perceived to be female as walking away. Furthermore, figures perceived to be gender-neutral also appeared more often, although not exclusively, to be walking towards observers

Walking direction triggers visuo-spatial orienting in 6-month-old infants and adults: An eye tracking study

a b s t r a c t The present study investigates whether the walking direction of a biological motion point-light display can trigger visuo-spatial attention in 6-month-old infants. A cueing paradigm and the recording of eye movements in a free viewing condition were employed. A control group of adults took part in the experiment. Participants were presented with a central point-light display depicting a walking human, followed by a single peripheral target. In experiment 1, the central biological motion stimulus depicting a walking human could be upright or upside-down and was facing either left or right. Results revealed that the latency of saccades toward the peripheral target was modulated by the congruency between the facing direction of the cue and the position of the target. In infants, as well as in adults, saccade latencies were shorter when the target appeared in the position signalled by the facing direction of the point-light walker (congruent trials) than when the target appeared in the contralateral position (incongruent trials). This cueing effect was present only when the biological motion cue was presented in the upright condition and not when the display was inverted. In experiment 2, a rolling point-light circle with unambiguous direction was adopted. Here, adults were influenced by the direction of the central cue. However no effect of congruency was found in infants. This result suggests that biological motion has a priority as a cue for spatial attention during development