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The predominant focus of my research is sensory processing in haptic perception. I am interested in how the perceptual qualities which are mostly associated with the sense of
touch are computed and represented in the brain. A good example to address these questions is research on softness perception. Softness is the subjective measure of an object's compliance (mm/N). Since there are no
mechanoreceptors directly responding to compliance, it is commonly assumed that softness perception occurs by combining information about the displacement of an object's surface and the information about the force being applied
to the object. Such information can be obtained from the cutaneous and kinesthetic afferent systems and in certain cases even from vision and audition. It is interesting how the information formed by different senses
is integrated and whether there is a common crossmodal representation of softness. The perception of softness is also extended over considerable time spans and offers an insight into the
integration of serial estimates. Furthermore, since several fingers might be involved in the exploration of softness it is interesting how the simultaneous
estimates from multiple fingers are processed. On top, I am interested in the role of top-down signals in haptic perception and bottom-up haptic saliency as compared to visual saliency.
2017 - now: Postdoctoral Researcher Justus-Liebig University Giessen
2015 - Summer School in Computational Sensory-Motor Neuroscience
2014 - 2017: PhD (Dr. rer. nat.) Justus-Liebig University Giessen
2011 - 2014: Applied research in Usability and Human-Computer-Interaction at eResult GmbH (consultancy), Göttingen
2017: PhD (Dr. rer. nat.) General Psychology at Justus-Liebig University Giessen
Thesis: Beyond a single touch: Sequential and top-down effects in haptic perception
2010: M.Sc. Cognitive Science at University of Osnabrück
Thesis: An adaptive model of human attention based on hierarchical feature complexity
2008: B.Sc. Biology at Leibniz University Hannover
Top-down modulation of shape and roughness discrimination in active touch by covert attention. Metzger, A., Mueller, S., Fiehler, K. & Drewing, K. (2018). Attention, Perception, Psychophysics.
Due to limitations in perceptual processing, information relevant to momentary task goals is selected from the vast amount of available sensory information by top-down mechanisms which can increase perceptual performance. We investigated how covert attention affects perception of 3D objects in active touch. In our experiment, participants simultaneously explored the shape and roughness of two objects in sequence, and were told afterwards to discriminate one of the two features. To direct the focus of covert attention to the different features we manipulated the expectation of a shape or roughness judgment by varying the frequency of trials for each task (20%, 50%, 80%) and measured discrimination thresholds. We found higher discrimination thresholds for both shape and roughness perception when the task was unexpected, compared to the conditions in which the task was expected (or both tasks were expected equally). Our results suggest that active touch perception is modulated by expectations about the task. This implies that despite fundamental differences, active and passive touch are affected by feature selective covert attention in a similar way.
Haptic Saliency Model for Rigid Textured Surfaces. Metzger, A., Toscani, M., Valsecchi,M. & Drewing, K. (2018). Haptics: Science, Technology, and Applications. EuroHaptics 2018.
When touching an object, we focus more on some of its parts rather than touching the whole object’s surface, i.e. some parts are more salient than others. Here we investigated how different physical properties of rigid, plastic, relieved textures determine haptic exploratory behavior. We produced haptic stimuli whose textures were locally defined by random distributions of four independent features: amplitude, spatial frequency, orientation and isotropy. Participants explored two stimuli one after the other and in order to promote exploration we asked them to judge their similarity. We used a linear regression model to relate the features and their gradients to the exploratory behavior (spatial distribution of touch duration). The model predicts human behavior significantly better than chance, suggesting that exploratory movements are to some extent driven by the low level features we investigated. Remarkably, the contribution of each predictor changed as a function of the spatial scale in which it was defined, showing that haptic exploration preferences are spatially tuned, i.e. specific features are most salient at different spatial scales.
Integration of serial sensory information in haptic perception of softness. Metzger, A., Lezkan, A. & Drewing, K. (2018). Journal of Experimental Psychology: Human Perception and Performance.
Redundant estimates of an environmental property derived simultaneously from different
senses or cues are typically integrated according to the maximum likelihood estimation model (MLE):
Sensory estimates are weighted according to their reliabilities, maximizing the percept"s reliability.
Mechanisms underlying the integration of sequentially derived estimates from one sense are less clear.
Here we investigate the integration of serially sampled redundant information in softness perception.
We developed a method to manipulate haptically perceived softness of silicone rubber stimuli during bare-finger exploration.
We then manipulated softness estimates derived from single movement segments (indentations) in a multisegmented
exploration to assess their contributions to the overall percept. Participants explored two stimuli in sequence,
using 2 to 5 indentations, and reported which stimulus felt softer. Estimates of the first stimulus"s softness contributed to
the judgments similarly, whereas for the second stimulus estimates from later compared to earlier indentations contributed
less. In line with unequal weighting, the percept"s reliability increased with increasing exploration length less than was
predicted by the MLE model. This pattern of results is well explained by assuming that the representation of the first
stimulus fades when the second stimulus is explored, which fits with a neurophysiological model of perceptual decisions
(Deco, Rolls, & Romo, 2010).
The longer the first stimulus is explored in softness discrimination the longer it can be compared to the second one. Metzger, A., & Drewing, K. (2017). World Haptics Conference (WHC), 2017 IEEE.
In haptic perception information is often sampled serially over a certain interval of time. For example, a stimulus is repeatedly indented to repeatedly estimate its softness. Albeit such redundant estimates are equally reliable, they seem to contribute differently to the overall haptic percept in a comparison task. When comparing the softness of two silicon rubber stimuli, the within-stimulus weights of estimates of the second stimulus' softness decrease during the exploration. Here we test the hypothesis that such decrease of weights depends on the representation strength of the first stimulus' softness. We varied the length of the first stimulus' exploration. Participants subsequently explored two silicon rubber stimuli by indenting the first stimulus (comparison) 1 or 5 times and the second stimulus (standard) always 3 times. We assessed the weights of indentation-specific estimates from the second stimulus by manipulating perceived softness during single indentations. Our results show that the longer the first stimulus is explored the more estimates of the second stimulus' softness can be included in the comparison of the two stimuli. This suggests that the exploration length of the first stimulus determines the strength of its representation which influences the decrease of weights of indentation-specific estimates of the second stimulus.
Haptic Aftereffect of Softness. Metzger, A., & Drewing, K. (2016). Haptics: Perception, Devices, Control, and Applications. EuroHaptics 2016.
Past sensory experience can influence present perception. We studied the effect of adaptation in haptic softness perception. Participants compared two silicon rubber stimuli, a reference and a comparison stimulus, by indenting them simultaneously with the index fingers of their two hands and decided which one felt softer. In adaptation conditions the index finger that explored the reference stimulus had previously been adapted to another rubber stimulus. The adaptation stimulus was indented 5 times with a force of >15 N, thus the two index fingers had a different sensory past. In baseline conditions there was no previous adaptation. We measured the Points of Subjective Equality (PSEs) of one reference stimulus to a set of comparison stimuli. We used four different adaptation stimuli, one was harder, two were softer and one had approximately the same compliance as compared to the reference stimulus. PSEs shifted as a function of the compliance of the adaptation stimulus: the reference was perceived to be softer when the finger had been adapted to a harder stimulus and it was perceived to be harder after adaptation to a softer stimulus. We conclude that recent sensory experience causes a shift of haptically perceived softness away from the softness of the adaptation stimulus. The finding that perceived softness is susceptible to adaptation suggests that there might be neural channels tuned to different softness values and softness is an independent primary perceptual quality.
Haptically perceived softness of deformable stimuli can be manipulated by applying external forces during the exploration. Metzger, A., & Drewing, K. (2015). World Haptics Conference (WHC), 2015 IEEE.
The perception of softness is the result of the integration of information provided by multiple cutaneous and kinesthetic signals. The relative contributions of these signals to the combined percept of softness was not yet addressed directly. We transmitted subtle external vertical forces to the exploring human finger during the exploration of deformable silicone rubber stimuli to dissociate the force estimates provided by the kinesthetic signals and the efference copy from cutaneous force estimates. This manipulation introduced a conflict between the cutaneous and the kinesthetic/efference copy information on softness. We measured Points of Subjective Equality (PSE) of manipulated references to stimuli which were explored without external forces. PSEs shifted as a linear function of external force in predicted directions - to higher compliances with pushing and to lower compliances with pulling force. We found relative contribution of kinesthetic/efference copy information to perceived softness being 23% for rather hard and 29% for rather soft stimuli. Our results suggest that an integration of the kinesthetic/efference copy information and cutaneous information with constant weights underlies softness perception. The kinesthetic/efference copy information seems to be slightly more important for the perception of rather soft stimuli.
Contributions in conferences
World Haptics Conference, 2015, Chicago, USA: Oral presentation. "Haptically perceived softness of deformable stimuli can be manipulated by applying external forces during the exploration."
European Conference on Visual Perception, 2016, Barcelona, Spain: Poster presentation. "Adaptation to softness in haptic perception."
World Haptics Conference, 2017, Fürstenfeldbruck (Munich), Germany: Oral presentation. "The longer the first stimulus is explored in softness discrimination the longer it can be compared to the second one."
Conference of Experimental Psychologists, 2017, Dresden, Germany: Oral presentation. "Serial integration of information in haptic softness perception."
Eurohaptics Conference, 2018, Pisa, Italy: Oral presentation. "Haptic Saliency Model for Rigid Textured Surfaces." Best paper award
Teaching & Supervision
Course: Perception: Theory and Application (held in German: Wahrnehmung: Grundlagen und Anwedung) (SS16)
Bachelor thesis: J. Schmidt: Meomory softness. (WS17)
Master thesis: S. Bruckbauer: Top-down influences on sensory processing in somatosensory texture and shape perception. (SS16)