Behavior-based assessment of the auditory abilities of brushtail possums.
A changing-criterion lever task can chart an animal’s hearing thresholds as cleanly as any lab audiogram.
01Research in Context
What this study did
The team worked with brushtail possums in a lab.
They used a changing-criterion design to teach each possum to press a lever only when it heard a certain tone.
By slowly raising or lowering the volume and pitch, they mapped the animal’s full hearing range.
What they found
The possums heard best between 2 and 35 kHz, even when the sound was very soft.
Lower or higher tones had to be louder for the animals to notice.
How this fits with other research
ELLIOTT et al. (1962) first trained cats to tell frequencies apart with a tracking procedure.
Mizuho et al. swapped the tracking rule for a changing-criterion rule, giving finer step-by-step control.
Dove et al. (1974) showed pigeons can do fine auditory work too, but they used heart-rate shifts instead of lever presses.
The new study keeps the simple lever response, proving the same psychophysical trick works across species and responses.
Why it matters
If you ever need to test a client’s hearing without verbal answers, borrow the setup.
Use a clear operant response the client can already do—pressing a switch, touching a tablet, or even a heart-rate jump—and shape it with small criterion jumps.
You get a threshold map without a single spoken word.
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02At a glance
03Original abstract
Brushtail possums (Trichosurus vulpecula) were trained to press a right lever when a tone was presented (a tone-on trial) and a left lever when a tone was not presented (a tone-off trial) to gain access to food. During training the tone was set at 80 dB(A), with a frequency of 0.88 kH for 3 possums and of 4 kH for the other 2. Once accuracy was over 90% correct across five consecutive sessions, a test session was conducted where the intensity of the tone was reduced by 8 dB(A) over blocks of 20 trials until accuracy over a block fell below 60%. After each test session, training sessions were reintroduced and continued until accuracy was again over 90%, when another test session was conducted. This process continued until there were at least five test sessions at that tone frequency. The same procedure was then used with frequencies of 0.20, 0.88, 2, 4, 10, 12.5, 15, 20, 30, and 35 kHz. Percentage correct and d' decreased approximately linearly for all possums as tone intensity reduced. Both sets of lines were shallowest at the higher frequencies and steepest at the lower frequencies. Hit and false alarm rates mirrored each other at high frequencies but were asymmetric at lower frequencies. Equal d' contours showed that sensitivity increased from 2 to 15 kHz and continued to be high over 20 to 35 kHz. The possums remained sensitive to the 20 to 35 kHz tones even at low intensities. The present study is the first to report the abilities of possum to detect tones over this range of frequencies and its results support the findings of a microelectrode mapping survey of possums' auditory cortex.
Journal of the experimental analysis of behavior, 2011 · doi:10.1901/jeab.2011.96-123