Scenario 9 – Hearing Abilities in Different Species

As part of your role investigating the limits of hearing in different species, you have been measuring absolute thresholds at a variety of different frequencies. You start with human subjects and make the following observations:

Test tone frequency (Hz)	50	200	1k	2k	5k	10k	15k
Absolute threshold (dB)	40	18	5	2	4	10	30

Plot the psychophysical function of hearing for this human group.

At which frequency are they most sensitive to sound?

Give an example of a sound they cannot hear? Be specific in terms of frequency and sound pressure level (dB).

You next examine hearing in a primate who has been trained to carry out psychophysical tasks. The data you collected from a small group of animals was as follows:

Test tone frequency (Hz)	50	200	1k	2k	5k	10k	15k
Absolute threshold (dB)	40	18	5	2	4	10	30

Plot the psychophysical function for the primates.

How do they differ from the human subjects you tested? What can you say about their perception of sound?

Give an example of a sound that primates can hear but humans cannot.

Given that primates cannot communicate what they perceive, how would you measure an absolute threshold? Briefly outline an approach that could be adopted with any species that is incapable of understanding instructions or providing a verbal response. By all means refer to examples from the literature.