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Biological motion perception-our capacity to perceive the intrinsic motion of humans and animals-has been implicated as a precursor of social development in infancy. In the adult brain, several biological motion neural correlates have been identified; of particular importance, the right posterior superior temporal sulcus (rpSTS).We present a study, conducted with fNIRS, which measured brain activations in infants' right posterior temporal region to point-light walkers, a standard stimulus category of biological motion perception studies.Seven-month-old infants (n = 23) participated in a within-subject blocked design with three experimental conditions and one baseline. Infants viewed: an intact upright point-light walker of a person approaching the observer; the same point-light walker stimulus but inverted; and a selected frame from the point-light walker stimulus, approaching the viewer at constant velocity with no articulated motion, close to object motion.We found activations for both the upright and the inverted point-light walkers. The rigid moving point-light walker frame did not elicit any response consistent with a functional activation in this region.Our results suggest that biological motion is processed differently in the right middle posterior temporal cortex in infancy, and that articulated motion is a critical feature in biological motion processing at this early age., This study was conducted at Psychology Research Center (UID/PSI/01662/2013), University of Minho, and supported by the Portuguese Foundation for Science and Technology and the Portuguese Ministry of Science, Technology and Higher Education through national funds and co-financed by FEDER through COMPETE2020 under the PT2020 Partnership Agreement (POCI-01-0145-FEDER-007653). This research was also supported by PhD grants from Portuguese Science and Technology Foundation to ICL (PD/BD/105966/2014), HM (SFRH/BD/86694/2012), and research grants PTDC/MHC-PCN/1530/2014 and IF/00217/2013 attributed to AP. This study was conducted at the Psychology Research Centre (PSI/01662), School of Psychology, University of Minho, supported by the Foundation for Science and Technology (FCT) through the Portuguese State Budget (Ref.: UIDB/PSI/01662/2020).

When people walk side-by-side, they often synchronize their steps. To achieve this, individuals might cross-modally match audiovisual signals from the movements of the partner and kinesthetic, cutaneous, visual and auditory signals from their own movements. Because signals from different sensory systems are processed with noise and asynchronously, the challenge of the CNS is to derive the best estimate based on this conflicting information. This is currently thought to be done by a mechanism operating as a Maximum Likelihood Estimator (MLE). The present work investigated whether audiovisual signals from the partner are integrated according to MLE in order to synchronize steps during walking. Three experiments were conducted in which the sensory cues from a walking partner were virtually simulated. In Experiment 1 seven participants were instructed to synchronize with human-sized Point Light Walkers and/or footstep sounds. Results revealed highest synchronization performance with auditory and audiovisual cues. This was quantified by the time to achieve synchronization and by synchronization variability. However, this auditory dominance effect might have been due to artifacts of the setup. Therefore, in Experiment 2 human-sized virtual mannequins were implemented. Also, audiovisual stimuli were rendered in real-time and thus were synchronous and co-localized. All four participants synchronized best with audiovisual cues. For three of the four participants results point toward their optimal integration consistent with the MLE model. Experiment 3 yielded performance decrements for all three participants when the cues were incongruent. Overall, these findings suggest that individuals might optimally integrate audiovisual cues to synchronize steps during side-by-side walking., info:eu-repo/semantics/publishedVersion

There is conflicting evidence about whether stimulus magnification is sufficient to equate the discriminability of point-light walkers across the visual field. We measured the accuracy with which observers could report the directions of point-light walkers moving +/-4 degrees from the line of sight, and the accuracy with which they could identify five different point-light walkers. In both cases accuracy was measured over a sevenfold range of sizes at eccentricities from 0 degrees to 16 degrees in the right visual field. In most cases observers (N=6) achieved 100% accuracy at the largest stimulus sizes (20 degrees height) at all eccentricities. In both tasks the psychometric functions at each eccentricity were shifted versions of each other on a log-size axis. Therefore, by dividing stimulus size at each eccentricity (E) by an appropriate F=1+E/E(2) (where E(2) represents the eccentricity at which stimulus size must double to achieve equivalent-to-foveal performance) all data could be fit with a single function. The average E(2) value was .91 (SEM=.19, N=6) in the walker-direction discrimination task and 1.34 (SEM=.21, N=6) in the walker identification task. We conclude that size scaling is sufficient to equate discrimination and identification of point-light walkers across the visual field.

© 2014 Troyer, Curley, Miller, Saygin and Bergen. Language comprehension requires rapid and flexible access to information stored in long-term memory, likely influenced by activation of rich world knowledge and by brain systems that support the processing of sensorimotor content. We hypothesized that while literal language about biological motion might rely on neurocognitive representations of biological motion specific to the details of the actions described, metaphors rely on more generic representations of motion. In a priming and self-paced reading paradigm, participants saw video clips or images of (a) an intact point-light walker or (b) a scrambled control and read sentences containing literal or metaphoric uses of biological motion verbs either closely or distantly related to the depicted action (walking). We predicted that reading times for literal and metaphorical sentences would show differential sensitivity to the match between the verb and the visual prime. In Experiment 1, we observed interactions between the prime type (walker or scrambled video) and the verb type (close or distant match) for both literal and metaphorical sentences, but with strikingly different patterns. We found no difference in the verb region of literal sentences for Close-Match verbs after walker or scrambled motion primes, but Distant-Match verbs were read more quickly following walker primes. For metaphorical sentences, the results were roughly reversed, with Distant-Match verbs being read more slowly following a walker compared to scrambled motion. In Experiment 2, we observed a similar pattern following still image primes, though critical interactions emerged later in the sentence. We interpret these findings as evidence for shared recruitment of cognitive and neural mechanisms for processing visual and verbal biological motion information. Metaphoric language using biological motion verbs may recruit neurocognitive mechanisms similar to those used in processing literal language but be represented in a less-specific way.

Assessing intentions, direction, and velocity of others is necessary for most daily tasks, and such information is often made available by both visual and auditory motion cues. Therefore, it is not surprising our great ability to perceive human motion. Here, we explore the multisensory integration of cues of biological motion walking speed. After testing for audiovisual asynchronies (visual signals led auditory ones by 30ms in simultaneity temporal windows of 76.4ms), in the main experiment, visual, auditory, and bimodal stimuli were compared to a standard audiovisual walker in a velocity discrimination task. Results in variance reduction conformed to optimal integration of congruent bimodal stimuli across all subjects. Interestingly, the perceptual judgments were still close to optimal for stimuli at the smallest level of incongruence. Comparison of slopes allows us to estimate an integration window of about 60ms, which is smaller than that reported in audiovisual speech., This work was partly funded by the Portuguese Foundation for Science and Technology (SFRH/BD/36345/2007, PTDC/SAU-BEB/68455/2006, SFRH/BSAB/974/2009) and the Portugal-Spain Actions PT2009-0186 from the Spanish Government and E-134/10 from the Portuguese Conselho de Reitores das Universidades Portuguesas.

There is evidence that human observers are more sensitive to the direction-of-heading of point-light walkers defined by first-order than second-order motions. We addressed this question by measuring the minimum direction difference (azimuth) that observers could discriminate when the dots composing the walkers were conveyed by first or second-order motions. Sensitivity to azimuth differences for four stimulus types (two first-order and two second-order) was tested at a range of stimulus sizes and at eccentricities of 0–16° in the right visual field. We find that for most stimulus types and eccentricities any azimuth threshold can be obtained by an appropriate adjustment of stimulus size. To achieve a given azimuth threshold second-order stimuli must be larger than the corresponding first-order stimuli. Therefore, stimulus magnification equates sensitivity to walker direction and we may say that sensitivity to walker direction is generally cue-independent. Similarly, in most cases stimulus magnification is sufficient to eliminate eccentricity dependent variability from the azimuth thresholds. Interestingly, the magnification required match peripheral to foveal thresholds increases faster with eccentricity for first-order stimuli than for second-order stimuli, while at the same time thresholds for first-order stimuli are lower than those for second-order stimuli at corresponding sizes and eccentricities.