Dynamics of walking adaptation aftereffects induced in static images of walking actors
Nick Barraclough, Jennifer Ingham and Stephen Page
Visual adaptation to walking actions results in subsequent aftereffects that bias perception of static images of walkers in different postures so that they are interpreted as walking in the opposite direction to the adapting actor. In order to test how walking aftereffects are comparable to other well studied low- and high-level visual aftereffects we measured walking aftereffect dynamics in order to assess the characteristics of the adapting mechanism. We found that walking aftereffects showed similar characteristic dynamics as for face aftereffects and some motion aftereffects. Walking aftereffects could be induced in a broad range of different static images of walking actors and were not restricted to images of actors in any particular posture. Walking aftereffects increased with adapting stimulus repetition and declined over time. The duration of the aftereffect was dependent upon time spent observing the adapting stimulus and could be well modelled by a power-law function that characterises this relationship in both face and motion aftereffects. Increasing the speed of the adapting stimulus by increasing actor walk speed increased aftereffect magnitude, as seen for some motion aftereffects. The nature of the aftereffects induced by observing walking actors indicates that they behave like traditional high-level visual aftereffects.
Emotion through point-light human locomotion: gender effects
Marina Pavlova, Samuel Krüger, Alexander N. Sokolov and Ingeborg Krägeloh-Mann
Body language reading is of importance for daily-life social cognition and successful social interaction. Yet it is unclear whether our ability for body language reading is gender dependent. In the present work, healthy female and male observers had to recognize emotions through point-light human locomotion performed by female and male actors with different emotional expressions (happy, angry, or neutral). For subtle emotional expressions, males surpass females in recognition of happy walking portrayed by female actors, whereas females tend to excel in recognition of hostile angry locomotion expressed by male actors. In contrast to widespread beliefs about female superiority in social cognition, the findings suggest that gender effects in recognition of emotions from human locomotion are modulated by emotional content of actions and (opposite) actor gender. The outcome is discussed in the light of recent work on gender effects in emotion recognition from point-light body motion [Alaerts et al, 2011, PLoS One, 6(6), e20989; Sokolov et al, 2011, Frontiers in Psychology, 2:16]. Overall, the study takes a further step in clarification of gender-related impairments in body language reading [Pavlova, 2012, Cerebral Cortex, 22(5), 981-995].
Structural connection between the cerebellum and temporal cortex underpinning biological motion processing
Arseny Sokolov, Michael Erb, Wolfgang Grodd and Marina Pavlova
Previous work in lesional patients suggests engagement of the left lateral cerebellum in visual processing of body motion [Sokolov et al, 2010, Cerebral Cortex, 20(2), 486-491]. Cerebellar involvement in the network dedicated to body motion processing appears to be mediated through two-way effective connectivity with the right superior temporal sulcus (STS) [Sokolov et al, 2012, Neuroimage, 59(3), 2824-2830]. Yet the underlying pattern of structural connectivity between the STS and cerebellum remains unknown. Here we address this issue by combining diffusion tensor imaging (DTI) with functional magnetic resonance imaging (fMRI). Participants viewed point-light biological motion and spatially scrambled displays while performing a one-back repetition task. Probabilistic tractography on individual seeds in the STS and left lateral cerebellum resulting from fMRI analysis revealed two structural connections forming a cerebello-temporal loop. The findings point to a structural pathway presumably underpinning communication between the STS and cerebellum during visual biological motion processing. This connection might also be of potential significance for other visual social functions.
Increased eccentricity reduces the contribution of form to the perception of biological motion
James Thompson, Sarah Dziura, Wendy Baccus and Ashley Safford
The perception of biological motion relies on the integration of form and motion cues, although assessing the contribution of each cue is difficult. We hypothesized that the contribution of form to perception of the facing direction of a point-light walker (PLW) would decrease as eccentricity increased at a faster rate than the contribution of motion. To test this, participants (n=14) reported the facing direction of a PLW that was walking forwards (FW) or backwards (BW). While form and motion can both be used for facing direction for FW, motion is incongruent with facing direction for BW, and accurate discrimination relies on form. PLWs were presented in random noise (65 dots), with a height subtending 7deg, at fixation and at 2, 4, 6, 8, and 10deg eccentricity. We found that eccentricity had a significantly greater effect on accuracy for BW than FW, especially for eccentricities of 2-4deg. These results suggest that increasing eccentricity has a greater effect on the contribution of form cues to the perception of biological motion than on the contribution of motion cues. This is consistent with the suggestion that the relative contribution of form and motion cues to biological motion perception depends on each cue's reliability.
How are facial expressions represented in the human brain?
Johannes Schultz, Ana Lucia Fernandez Cruz, Stephan de La Rosa, Heinrich Bülthoff and Kathrin Kaulard
The dynamic facial expressions that we encounter every day can carry a myriad of social signals. What are the neural mechanisms allowing us to decode these signals? A useful basis for this decoding could be representations in which the facial expressions are set in relation to each other. Here, we compared the behavioral and neural representations of 12 facial expressions presented as pictures and videos. Behavioral representations of these expressions were computed based on the results of a semantic differential task. Neural representations of these expressions were obtained by multivariate pattern analysis of functional magnetic imaging data. The two kinds of representations were compared using correlations. For expression videos, the results show a significant correlation between the behavioral and neural representations in the superior temporal sulcus (STS), the fusiform face area, the occipital face area and the amygdala, all in the left hemisphere. For expression pictures, a significant correlation was found only in the left STS. These results suggest that of all tested regions, the left STS contains the neural representation of facial expressions that is closest to their behavioral representation. This confirms the predominant role of STS in coding changeable aspects of faces, which includes expressions.
Coherent form, motion and biological motion perception in congenital achromatopsia
Eliza A Burton, John Wattam-Bell, Michel Michaelides, Koji M Nishiguchi, Venki Sundaram, Andrew R Webster, Anthony T Moore and Marko Nardini
In congenital achromatopsia there is an absence of functioning cone photoreceptors, so that from birth vision is entirely reliant on rods. The impact of this on extrastriate visual functions such as coherent form and motion perception has not previously been explored. In healthy controls, rod-mediated perception as assessed under scotopic conditions showed normal coherent motion thresholds, but increased form-from-motion and biological motion thresholds [Gegenfurtner et al, 2000, JOSA A, 17(9), 1505-1515; Grossman and Blake, 1999, Vision Res, 39(22), 3721-3727]. We measured coherence thresholds using 2AFC for circular form, rotating motion and biological motion in achromats (n=3) and controls (n=5) under scotopic and mesopic conditions. In both groups, form and biological motion thresholds increased scotopically, while motion remained stable. At both light levels, thresholds for form and motion, but not biological motion, were higher in achromats than in controls. The results indicate that congenital absence of functioning cones leads to deficits in coherent form and motion perception even at scotopic light levels. This implies that cone pathways play a role in development of rod-mediated extra-striate processing. Achromats’ increased thresholds under scotopic vs mesopic conditions suggest differential involvement of visual pathways (e.g. fast vs slow rod pathway) in the two conditions.