Scenario 6 – Collision Warning Perception

As part of your work in the Human Factors Department of a car manufacturing company, you are investigating the parameters necessary for a sound inside the car to be perceived as an urgent warning. As a preliminary exercise, you started by looking at the sound frequency (although you also plan to look at sound duration, number of pulses within the sound etc). You recruited a number of regular drivers to take part in an experiment that uses the Method of Adjustment. Your volunteers adjusted the frequency of a sound in both ascending and descending trials to a point where they perceived this as an "urgent warning". The following is a set of measurements made from one of your volunteers:

Trial Number	1	2	3	4	5	6	7	8	9	10	11	12
Sound frequency (Hz)	24	20	24	21	19	19	21	20	26	25	18	17

Calculate the threshold sound frequency.

Why did you have two different types of trials (one starting with low frequencies, and the other starting with higher frequencies)?

If you had been calculating difference thresholds, which statistical value would provide an estimate of that threshold?

Comment on how accurate this threshold estimate is relative to estimates derived by other methods. If you wanted the most accurate estimate of the threshold sound frequency, outline an approach you might have adopted.