The mouse enters the left compartment and listens for the tone. After a variable waiting period, a tone burst is presented and the mouse crosses to the right compartment to activate a mechanical dipper that delivers a water reward. If the mouse crosses the barrier before the tone, or waits too long to cross, water is not delivered and the testing sequence is interrupted by a time out interval. Catch trials with no tone presentations are presented at random intervals to monitor the frequency of guessing. This figure shows absolute hearing thresholds as a function of frequency for laboratory mice.
Different symbols indicate results from four previous studies using a variety of testing procedures.
Maximum sensitivity is noted as a dip in the curve at frequencies around 16 kHz. This young animal exhibits normal sensitivity. Psychometric functions plot the percentage of correct barrier crossings in relation to the loudness levels of 8-kHz tone bursts. Sensitivity to environmental noise Environmental noise represents a serious challenge to hearing-impaired listeners. In the left panel of the figure, psychometric functions appear to be similar for testing in quiet and moderate background noise, but note the subject's higher percentage of false alarms in noise.