Variability in the rigid pinna motions of hipposiderid bats and their impact on sensory information encoding

Abstract

Many bat species, e.g., in the rhinolophid and hipposiderid families, have dynamic biosonar systems with highly mobile pinnae. Pinna motion patterns have been shown to fall into two distinct categories: rigid rotations and non-rigid motions (i.e., deformations). In the present work, two questions regarding the rigid rotations have been investigated: (i) what is the nature of the variability (e.g., discrete subgroups or continuous variation) within the rigid motions, (ii) what is its acoustic impact? To investigate the first question, rigid pinna motions in Pratt's leaf-nosed bats (Hipposideros pratti) have been tracked with stereo vision and a dense set of landmark points on the pinna surface. Axis-angle representations of the recorded rigid motions have shown a continuous variation in the rotation axes that covered a range of almost 180° in azimuth and elevation. To investigate the second question, the observed range of rigid pinna motions has been reproduced with a biomimetic pinna. Normalized mutual information between acoustic inputs associated with every pair of the rigid pinna motions showed that even small changes in the rotation axis resulted in more than 50% new sensory information encoding capacity (i.e., normalized mutual information less than 50%). This demonstrates a potential sensory benefit to the observed variability in the rigid pinna rotations.

Theoretical investigation of active listening behavior based on the echolocation of CF-FM bats

“…Rhinolophidae and Hipposideridae families synchronize the movement of their left and right pinnae with pulse emission [19][20][21][22]. This active listening behavior has been reported for constant frequency-frequency modulated (CF-FM) bats, who use a compound signal consisting of a CF part and an FM part (Fig 1A).…”

Theoretical investigation of active listening behavior based on the echolocation of CF-FM bats

“…Several species of bats employ behavioral solutions for echo source direction detection. The Rhinolophidae and Hipposideridae families synchronize the movement of their left and right pinnae with the pulse emissions [19][20][21][22]. This active listening behavior has been reported for constant frequency-frequency modulated (CF-FM) bats, who use a compound signal consisting of a CF part and an FM part (Fig 1A).…”

Biomimetic detection of dynamic signatures in foliage echoes

“…to alternate between rigid and non rigid motions [107] and have been shown to possess a large range of variability at least in the rigid motions [108]. Hence, it may be hypothesized that this variability provides a substrate for adaptation that would allow the animals to encode more useful sensory information.…”

“…The biomimetic sonarhead in our experiment used the same simplified pinna and noseleaf motions for the entire dataset, however bats are known to be capable of different types of movements, classified as rigid and non rigid [107]. It has also been shown that the rigid motions show a large range of variability in the rigid motions [108]. Therefore the potential exists for different motions to be adapted to specific tasks which could enable greater information encoding within foliage echoes.…”