We have to remember that what we observe is not nature in itself but nature exposed to our method of questioning

Werner Karl Heisenberg

Contact Information

E-mail:       aytekin@umd.edu
Telephone:   301-405-0374 (batlab)

Degrees, Positions

Research Interests

As being a biological airborne sonar system a bat accomplishes target detection, identification, localization, tracking and finally capturing or avoiding. Engineered radar/sonar systems designed to realize only a subset of these functions in a limited capability. Bats seem to be very adaptive to the changing environmental conditions in degree to which engineered systems currently cannot achieve. In order to design systems that can be capable behaving in complex environments, bats could be ideal model system to study.

My research interest mainly in two related directions in bat echolocation: Bats monitor their environment by making ultrasonic vocalizations and listening to echoes reflected from objects in the scene. Localizing the position of an object essential for bats survival. Echoes acoustically interact with the head and external ear in a direction-dependent sense. The transformation as a result of this interaction creates the physical cues necessary to localize the source of the echo. The direction dependent transformations can simply be modeled as time-independent transfer functions of linear systems. The project I am involved in aims to measure and analyze these transfer functions, also known as head related transfer functions (HRTF), to understand more about sound localization by bats. I investigate the cues for sound localization that are likely to be used by evaluating frequency structure of the HRTFs. Hypothesis as a result of these investigations are tested via psychoacoustical experiments involving echolocating bats. Some interesting results of this research can be found here.

I am also employing computational methods to understand how the auditory system might compute sound localization. An example of these efforts is a binaural model for sound localization based on the bat HRTF to show that bats can use interaural level difference (ILD) cues to localize sound sources. Pursuing this avenue brought up an interesting question which motivates the computational part of my research. How an initially naïve, - unfamiliar to spatial nature of the sound - animal could learn to localize sound sources? Unlike the common approaches in sound localization modeling that assume availability of the acoustic cues for sound location, my approach attemps to circumvent the need for this assumption and ground the problem of auditory space learning. This approach employs sensorimotor contingencies for the learning of the auditory space. More detail about this approach and its motivation can be found here (see also a related lay language paper here).

A second set of studies aims to understand the spatial properties of the bats' outgoing sonar calls. The goal of these studies is to measure the sonar beam profile across the frequency range of 20 kHz to 100 kHz from a freely behaving echolocating bat. Unlike the earlier studies on this species this study employs a different approach which allows sonar beam pattern measurements without requiring restraining of the bat and electrical stimulation of the brain stem to elicit sonar vocalizations. My preliminary studies suggest that the outgoing ultrasound beamshape of a bat is not constant but varies from vocalization to vocalization. Follow up studies are focusing on how the sonar beamshape changes and whether or not this change is controlled by the bat and if so what are the implications for echolocation.

Publications

JOURNALS

M. Aytekin, C.F. Moss and J. Z. Simon (2008), A sensorimotor Approach to Sound Localization, Neural Computation, Vol. 20, No. 3: 603–635. [PDF]

M. Aytekin, E. Grassi, C.F. Moss and M. Sahota (2004), The Head-related Transfer Function Reveals Binaural Cues For Sound Localization J. Acoust. Soc. Am. 116(6). [PDF]

CONFERENCE

Posters

M. Aytekin, C.F. Moss  “A sensorimotor model of sound localization in the echolocating bat, Eptesicus fuscus” ARO 2005 Mid-winter Meeting.

B. Falk, T. Williams, M. Aytekin, K. Ghose and C.F. Moss "Texture discrimination by echolocation: acoustics and behavior" Society for Neuroscience, 2005 Annual Meeting.

M. Aytekin, C.F. Moss  “Interaural Level Difference Based Sound Localization by Bats” Society for Neuroscience, 2004 Annual Meeting.

M. Aytekin, C.F. Moss “Sound localization with binaural cues in echolocating bat, Eptesicus fuscus” 1^st International Conference on Acoustic Communication by Animals.

 M. Aytekin, C.F. Moss “A Neural Network Sound Localization Model of Echolocating Bat, Eptesicus fuscus” ARO 2002 Mid-winter Meeting

 M. Aytekin, E. Grassi, M. Sahota, C.F. Moss "Acoustic transfer function of the echolocating bat, Eptesicus fuscus" ARO 2001 Mid-winter Meeting.

THESIS

"Direction of Arrival Estimation and Spatial-Temporal Filtering with Adaptive Sensor Arrays" (M.S. Thesis, Yildiz Technical University, 1998)

"Sound Localization by Echolocating Bats" (Ph.D. Thesis, University of Maryland , 2007)

My References