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Animal Psychoacoustics
Perception of the Auditory Scene
Like humans, animals are often bombarded by signals com- ing from multiple directions, all hitting the auditory system at the same time and often obscured by noise. They must extract separate auditory objects from the complex acous- tic waveform on the basilar membrane. Humans have no problem telling you that a clock is ticking to the left, a fan is whirring overhead, and a person is talking to them from the other room, even though these signals overlap in time, space, and frequency. We would call these objects separate auditory “streams.” We know less about how animals do this sort of segregation of auditory objects, but researchers are interested in whether this is common across animals. The techniques used are often more complicated than simply asking an animal if something is there or not, as in a de- tection task, or to discriminate between two sounds. Often, animals are trained to identify one stimulus or two (Christi- son-Lagay and Cohen, 2014), whether the sounds are over- lapping or alternating (Neilans and Dent, 2015), or, in the case of bottlenose dolphins, to identify an object.
Bottlenose dolphins can recognize objects using “intersen- sory recognition.” That is, when a sample object is visually presented to them, they can use their echolocation signals to match the object they saw. Conversely, if an auditory echo- location signal is presented to them and then the sample objects are acoustically shielded, they can use their vision to identify the object they heard (Pack and Herman, 1995). This intersensory recognition ability is likely prevalent in echolocating bats (e.g., Eklof and Jones, 2003), but comple- mentary studies have not yet been conducted.
Biosketch
Goldfish use frequency differences in stimuli for separating auditory objects into separate acoustic streams (Fay, 2000). Gray treefrogs (Hyla chrysoscelis) segregate frog advertise- ment calls from a chorus of other calls using spatial cues, much in the way humans are able to hear a signal at a cock- tail party (Bee, 2007). These studies and many others tell us about the limits of the resolving power of animals in com- plex listening environments and suggest that animals orga- nize their world in similar ways as humans.
Localization
To learn about sound localization in animals, another com- mon animal psychoacoustics measure, see the recent article in Acoustics Today by Heffner and Heffner (2016). Sound lo- calization is extremely important for survival in the animal
world. Prey need to know which direction the predator is coming from in order to escape capture. Predators need to be able to pinpoint a prey item quickly and accurately be- fore they are noticed or they will not eat. As with audiogram variability across vertebrates, localization acuity also varies widely across the animal kingdom and has been the subject of many animal psychophysical experiments.
Conclusions
Although some measures such as auditory brainstem re- sponses, single-cell recordings, and acoustic startle are much quicker than animal psychophysical studies (which can take weeks, months, or even years to complete), many studies have found large differences between results from operant and untrained indirect reflexive measures of hearing like the startle response (e.g., Lauer et al., 2017) and evoked physi- ological and operant thresholds (e.g., Sisneros et al., 2016). These differences suggest that researchers should take the time to conduct psychoacoustic experiments in awake, be- having, trained, and reliable animal observers to assess the auditory world of animals with accuracy. Furthermore, al- though measurements of hearing in complex acoustic envi- ronments may seem daunting to some, they are important for helping us create scientifically backed decisions for envi- ronmental noise control and development.
Acknowledgments
Special thanks to Dr. Robert Dooling, a tremendous men- tor and friend. The laboratory is supported by Grant DC- 0012302 from the National Institute on Deafness and Other Communication Disorders, National Institutes of Health.
Micheal Dent is a professor in the De- partment of Psychology at the Univer- sity at Buffalo, State University of New York. After obtaining a PhD in integra- tive neuroscience from the University of Maryland at College Park, she worked as a postdoctoral research scientist at the
University of Wisconsin Medical School before going to Buf- falo in 2004. She serves on the editorial boards of The Journal of the Acoustic Society of America, Proceedings of Meetings on Acoustics, and Acoustics Today. Dr. Dent studies acoustic communication in mice and birds using psychoacoustics, vocalization recordings, and preference techniques.
24 | Acoustics Today | Fall 2017