Daniel Jokisch

Structural encoding and recognition of biological motion: evidence from event-related potentials and source analysis.

In the present study, we investigated how different processing stages involved in the perceptual analysis of biological motion (BM) are reflected by modulations in event-related potentials (ERP) in order to elucidate the time course and location of neural processing of BM. Data analysis was carried out using conventional averaging techniques as well as source localization with low resolution brain electromagnetic tomography (LORETA). ERPs were recorded in response to point-light displays of a walking person, an inverted walking person and displays of scrambled motion. Analysis yielded a pronounced negativity with a peak at 180 ms after stimulus onset which was more pronounced for upright walkers than for inverted walkers and scrambled motion. A later negative component between 230 and 360 ms after stimulus onset had a larger amplitude for upright and inverted walkers as compared to scrambled walkers. In the later component, negativity was more pronounced in the right hemisphere revealing asymmetries in BM perception. LORETA analysis yielded evidence for sources specific to BM within the right fusiform gyrus and the right superior temporal gyrus for the second component, whereas sources for BM in the early component were located in areas associated with attentional aspects of visual processing. The early component might reflect the pop-out effect of a moving dot pattern representing the highly familiar form of a human figure, whereas the later component might be associated with the specific analysis of motion patterns providing biologically relevant information.

Biological motion as a cue for the perception of size

Animals as well as humans adjust their gait patterns in order to minimize energy required for their locomotion. A particularly important factor is the constant force of earths gravity. In many dynamic systems, gravity defines a relation between temporal and spatial parameters. The stride frequency of an animal that moves efficiently in terms of energy consumption depends on its size. In two psychophysical experiments, we investigated whether human observers can employ this relation in order to retrieve size information from point-light displays of dogs moving with varying stride frequencies across the screen. In Experiment 1, observers had to adjust the apparent size of a walking point-light dog by placing it at different depths in a three-dimensional depiction of a complex landscape. In Experiment 2, the size of the dog could be adjusted directly. Results show that displays with high stride frequencies are perceived to be smaller than displays with low stride frequencies and that this correlation perfectly reflects the predicted inverse quadratic relation between stride frequency and size. We conclude that biological motion can serve as a cue to retrieve the size of an animal and, therefore, to scale the visual environment.

Differential involvement of the cerebellum in biological and coherent motion perception

Perception of biological motion (BM) is a fundamental property of the human visual system. It is as yet unclear which role the cerebellum plays with respect to the perceptual analysis of BM represented as point‐light displays. Imaging studies investigating BM perception revealed inconsistent results concerning cerebellar contribution. The present study aimed to explore the role of the cerebellum in the perception of BM by testing the performance of BM perception in patients suffering from circumscribed cerebellar lesions and comparing their performance with an age‐matched control group. Perceptual performance was investigated in an experimental task testing the threshold to detect BM masked by scrambled motion and a control task testing the detection of motion direction of coherent motion masked by random noise. Results show clear evidence for a differential contribution of the cerebellum to the perceptual analysis of coherent motion compared with BM. Whereas the ability to detect BM masked by scrambled motion was unaffected in the patient group, their ability to discriminate the direction of coherent motion in random noise was substantially affected. We conclude that intact cerebellar function is not a prerequisite for a preserved ability to detect BM. Because the dorsal motion pathway as well as the ventral form pathway contribute to the visual perception of BM, the question of whether cerebellar dysfunction affecting the dorsal pathway is compensated for by the unaffected ventral pathway or whether perceptual analysis of BM is performed completely without cerebellar contribution remains to be determined.

The neural coding of expected and unexpected monetary performance outcomes: Dissociations between active and observational learning

Successful adaptation to the environment requires the learning of stimulus-response-outcome associations. Such associations can be learned actively by trial and error or by observing the behaviour and accompanying outcomes in other persons. The present study investigated similarities and differences in the neural mechanisms of active and observational learning from monetary feedback using functional magnetic resonance imaging. Two groups of 15 subjects each - active and observational learners - participated in the experiment. On every trial, active learners chose between two stimuli and received monetary feedback. Each observational learner observed the choices and outcomes of one active learner. Learning performance as assessed via active test trials without feedback was comparable between groups. Different activation patterns were observed for the processing of unexpected vs. expected monetary feedback in active and observational learners, particularly for positive outcomes. Activity for unexpected vs. expected reward was stronger in the right striatum in active learning, while activity in the hippocampus was bilaterally enhanced in observational and reduced in active learning. Modulation of activity by prediction error (PE) magnitude was observed in the right putamen in both types of learning, whereas PE related activations in the right anterior caudate nucleus and in the medial orbitofrontal cortex were stronger for active learning. The striatum and orbitofrontal cortex thus appear to link reward stimuli to own behavioural reactions and are less strongly involved when the behavioural outcome refers to another persons action. Alternative explanations such as differences in reward value between active and observational learning are also discussed.

Evaluation-related frontocentral negativity evoked by correct responses and errors

An event-related potential (ERP) with frontocentral negativity is known to be evoked by error responses, but may also occur on correct response trials. The error-related negativity (ERN) is thought to be generated in the anterior cingulate cortex (ACC). The current study aimed to further elucidate its functional significance as well as its neuronal correlates by directly comparing its amplitude and time course on correct and error trials in a continuous performance task (CPT). Results yielded a frontocentral positive potential preceding correct responses and a high amplitude post-response frontocentral negative potential during conditions involving response competition. To remove potential no-confounding effects of the positive component preceding the motor response, a second experiment was conducted where a red fixation cross served as a cue for potential response competition tendencies. Again, results yielded highest post-response amplitudes on correct trials involving response competition. The positive pre-response potential was eliminated by the visual cue. Interestingly, the cue led to an enhancement of the negative post-response component on trials without response competition. Taken together, the frontocentral post-response negativity might reflect evaluative rather than error-related processing.

Biological motion as a cue for the perception of absolute size

Gravity is a constant force that affects motion in the physical world. This is particularly true for animate motion, since animals try to energetically optimize their gait by shifting energy between different states such as kinetic, potential, and elastic energy. Constant gravity defines a fixed relation between temporal and spatial measures in motions such as pendulum motion and ballistic motion. In a psychophysical experiment, we tested whether the human visual system can retrieve size information mediated by gravity from dynamic point-light displays of animal locomotion.

Inversion effects on the structural encoding and recognition of biological motion

By representing the main joints of a person’s body by bright dots against a dark background, observers can easily recognize a human walker and determine his/her gender, recognize various action patterns and identify individual persons. The importance of the perception of biologically relevant motion patterns is reflected by the identification of a specific neural circuitry as shown by brain imaging studies. Whereas basic principles of the neural basis of perception of biological motion are understood, many issues concerning the temporal characteristics of the processing of such kind of information are as yet unclear.

Biological motion versus coherent motion perception: The role of the cerebellum

Perception of biological motion is a fundamental property of the human visual system. It is as yet unclear which role the cerebellum plays with respect to the perceptual analysis of biological motion represented as point-light displays. Imaging studies investigating biological motion perception revealed inconsistent results concerning cerebellar contribution. The present study aims to explore the role of the cerebellum in the perception of biological motion by testing the performance of biological motion perception in patients suffering from circumscribed cerebellar lesions and comparing their performance with an age-matched control group. Perceptual performance was investigated in an experimental task testing the threshold to detect biological motion masked by scrambled motion and a control task testing detection of motion direction of coherent motion masked by random noise. Results show clear evidence for a differential contribution of the cerebellum to the perceptual analysis of coherent motion compared to biological motion. Whereas the ability to detect biological motion masked by scrambled motion was unaffected in the patient group, their ability to discriminate direction of coherent motion in random noise was substantially affected. We conclude that intact cerebellar function is not a prerequisite for a preserved ability to detect biological motion. Since the dorsal motion pathway as well as the ventral form pathway contribute to the visual perception of biological motion, the question remains open, whether cerebellar dysfunction affecting the dorsal pathway is compensated for by the not affected ventral pathway or whether perceptual analysis of biological motion is performed completely without cerebellar contribution.