Tone deafness is associated with deficits in spatial processing

Representations of pitch and space in the brain seem to interact. An article from Douglas & Bilkey in Nature Neuroscience (PDF here) now reports that people with amusia, a pitch processing deficit, do not show the interference between these concepts that is found in control subjects. The abstract:

Amusia (commonly referred to as tone-deafness) is a difficulty in discriminating pitch changes in melodies that affects around 4% of the human population. Amusia cannot be explained as a simple sensory impairment. Here we show that amusia is strongly related to a deficit in spatial processing in adults. Compared to two matched control groups (musicians and non-musicians), participants in the amusic group were significantly impaired on a visually presented mental rotation task. Amusic subjects were also less prone to interference in a spatial stimulus-response incompatibility task and performed significantly faster than controls in an interference task in which they were required to make simple pitch discriminations while concurrently performing a mental rotation task. This indicates that the processing of pitch in music normally depends on the cognitive mechanisms that are used to process spatial representations in other modalities.

Here is a graphic from the review of this work by Janata in the same issue of Nature Neuroscience.

Figure... The link between musical and spatial processing was investigated via a set of tasks. (a) In a stimulus-response compatibility task, subjects press either the closer or farther of two buttons on a computer keyboard to indicate whether the second of two pitches is higher or lower than the first. The response that the second pitch was higher was made more quickly, on average, when the answer "higher pitch" was mapped to the 'higher' (farther) of the two response buttons, than when the response "lower pitch" was mapped to the higher button. (b) In the contour violation task from the Montreal Battery for the Evaluation of Amusia, subjects have to detect whether a single note in the repetition of a melody changed direction. Amusic individuals have extraordinary difficulty with this task. (c) In the Shepard and Metzler mental rotation task, subjects must determine whether two geometric figures are the same or different. (d) In the animal matching task, a large set of 15 animal pictures is shown to the subject along with a set of three probe pictures. Subjects must determine whether all three pictures from the small set are in the large set.