Johannes Lohmann

Balanced echo state networks

This paper investigates the interaction between the driving output feedback and the internal reservoir dynamics in echo state networks (ESNs). The interplay is studied experimentally on the multiple superimposed oscillators (MSOs) benchmark. The experimental data reveals a dual effect of the output feedback strength on the network dynamics: it drives the dynamic reservoir but it can also block suitable reservoir dynamics. Moreover, the data shows that the reservoir size crucially co-determines the likelihood of generating an effective ESN. We show that dependent on the complexity of the MSO dynamics somewhat smaller networks can yield better performance. Optimizing the output feedback weight range and the network size is thus crucial for generating an effective ESN. With proper parameter choices, we show that it is possible to generate ESNs that approximate MSOs with several orders of magnitude smaller errors than those previously reported. We conclude that there appears to be still much more potential in ESNs than previously thought and sketch-out some promising future research directions.

Behavioral Bias for Food Reflected in Hand Movements: A Preliminary Study with Healthy Subjects

Palatable food induces general approach tendencies when compared to nonfood stimuli. For eating disorders, the modification of an attention bias toward food was proposed as a treatment option. Similar approaches have been efficient for other psychiatric conditions and, recently, successfully incorporated approach motivation. The direct impact of attentional biases on spontaneous natural behavior has hardly been investigated so far, although actions may serve as an intervention target, especially seeing the recent advances in the field of embodied cognition. In this study, we addressed the interplay of motor action execution and cognition when interacting with food objects. In a Virtual Reality (VR) setting, healthy participants repeatedly grasped or warded high-calorie food or hand-affordant ball objects using their own dominant hand. This novel experimental paradigm revealed an attention-like bias in hand-based actions: 3D objects of food were collected faster than ball objects, and this difference correlated positively with both individual body mass index and diet-related attitudes. The behavioral bias for food in hand movements complements several recent experimental and neurophysiological findings. Implications for the use of VR in the treatment of eating-related health problems are discussed.

Modeling the temporal dynamics of visual working memory

Visual working memory (VWM) is one of the most crucial parts of the human cognitive system. Research focuses on the apparent limits in the capacity of this system and the reasons for them. So far only a few formal models exist that can account for the temporal dynamics of the amount of information stored in VWM. We propose a combination of the well established theory of visual attention (TVA) with a dynamic memory model, resulting in an iterative, probabilistic framework for VWM. The model includes a consolidation as well as a decay mechanism and employs the strength concept to quantify the availability of a certain memory trace. We evaluate the model on available change detection data.

Mental space maps into the future

It has been suggested that our mind anticipates the future to act in a goal-directed, event-oriented manner. Here we asked whether peripersonal hand space, that is, the space surrounding ones hands, is dynamically and adaptively mapped into the future while planning and executing a goal-directed object manipulation. We thus combined the crossmodal congruency paradigm (CCP), which has been used to study selective interactions between vision and touch within peripersonal space, with an object manipulation task. We expected crossmodal interactions in anticipation of the upcoming, currently planned object grasp, which varied trial-by-trial depending on the objects orientation. Our results confirm that visual distractors close to the future finger positions selectively influence vibrotactile perceptions. Moreover, vibrotactile stimulation influences gaze behavior in the light of the anticipated grasp. Both influences become apparent partly even before the hand starts to move, soon after visual target object onset. These results thus support theories of event encodings and anticipatory behavior, showing that peripersonal hand space is flexibly remapped onto a future, currently actively inferred hand position.

In touch with mental rotation: interactions between mental and tactile rotations and motor responses

Although several process models have described the cognitive processing stages that are involved in mentally rotating objects, the exact nature of the rotation process itself remains elusive. According to embodied cognition, cognitive functions are deeply grounded in the sensorimotor system. We thus hypothesized that modal rotation perceptions should influence mental rotations. We conducted two studies in which participants had to judge if a rotated letter was visually presented canonically or mirrored. Concurrently, participants had to judge if a tactile rotation on their palm changed direction during the trial. The results show that tactile rotations can systematically influence mental rotation performance in that same rotations are favored. In addition, the results show that mental rotations produce a response compatibility effect: clockwise mental rotations facilitate responses to the right, while counterclockwise mental rotations facilitate responses to the left. We conclude that the execution of mental rotations activates cognitive mechanisms that are also used to perceive rotations in different modalities and that are associated with directional motor control processes.

Lost in space: multisensory conflict yields adaptation in spatial representations across frames of reference

According to embodied cognition, bodily interactions with our environment shape the perception and representation of our body and the surrounding space, that is, peripersonal space. To investigate the adaptive nature of these spatial representations, we introduced a multisensory conflict between vision and proprioception in an immersive virtual reality. During individual bimanual interaction trials, we gradually shifted the visual hand representation. As a result, participants unknowingly shifted their actual hands to compensate for the visual shift. We then measured the adaptation to the invoked multisensory conflict by means of a self-localization and an external localization task. While effects of the conflict were observed in both tasks, the effects systematically interacted with the type of localization task and the available visual information while performing the localization task (i.e., the visibility of the virtual hands). The results imply that the localization of one’s own hands is based on a multisensory integration process, which is modulated by the saliency of the currently most relevant sensory modality and the involved frame of reference. Moreover, the results suggest that our brain strives for consistency between its body and spatial estimates, thereby adapting multiple, related frames of reference, and the spatial estimates within, due to a sensory conflict in one of them.

How Deep Is Your SNARC? Interactions Between Numerical Magnitude, Response Hands, and Reachability in Peripersonal Space

Spatial, physical, and semantic magnitude dimensions can influence action decisions in human cognitive processing and interact with each other. For example, in the spatial-numerical associations of response code (SNARC) effect, semantic numerical magnitude facilitates left-hand or right-hand responding dependent on the small or large magnitude of number symbols. SNARC-like interactions of numerical magnitudes with the radial spatial dimension (depth) were postulated from early on. Usually, the SNARC effect in any direction is investigated using fronto-parallel computer monitors for presentation of stimuli. In such 2D setups, however, the metaphorical and literal interpretation of the radial depth axis with seemingly close/far stimuli or responses are not distinct. Hence, it is difficult to draw clear conclusions with respect to the contribution of different spatial mappings to the SNARC effect. In order to disentangle the different mappings in a natural way, we studied parametrical interactions between semantic numerical magnitude, horizontal directional responses, and perceptual distance by means of stereoscopic depth in an immersive virtual reality (VR). Two VR experiments show horizontal SNARC effects across all spatial displacements in traditional latency measures and kinematic response parameters. No indications of a SNARC effect along the depth axis, as it would be predicted by a direct mapping account, were observed, but the results show a non-linear relationship between horizontal SNARC slopes and physical distance. Steepest SNARC slopes were observed for digits presented close to the hands. We conclude that spatial-numerical processing is susceptible to effector-based processes but relatively resilient to task-irrelevant variations of radial-spatial magnitudes.