Cognitive deficits in depression arise among others in the auditory domain [1
]. Thus, some authors considered impaired auditory processing as a potential marker for depression [2
]. There is a controversy, however, whether cognitive dysfunctions in depression are specific [4
] or general [5
]. Variable findings of correlations between depression and pitch perception may indicate the involvement of specific impairments: depressive patients responded less [1
], similarly [7
], or even more accurately [8
] than healthy controls in pitch perception tasks. The variable outcomes suggest that heterogeneous processes may be differentially affected during a depressive episode. The present study aimed to confirm that a specific pitch perception skill - pitch identification - and not pitch perception in general is impaired in depressive patients.
Three different skills contribute to pitch perception: pitch identification, pitch contour perception, and pitch discrimination [9
]. There are reasons to hypothesize that depression impairs specifically pitch identification: Pitch identification was assessed using a choice reaction task [11
], and visual choice reaction was poor in depression [6
]. Moreover, pitch identification activated the intraparietal sulcus which was associated with numerosity encoding [11
], and non-verbal encoding strategies were impaired in depressive patients [14
]. In contrast, little data support that depression affects pitch contour perception or pitch discrimination.
The test design can bias outcomes in a clinical study. For instance, too easily distinguishable pitches could level out differences due to a ceiling effect. A ceiling effect may explain why Knott et al. found no impairment of auditory perception in depression [7
]. Indeed, depressive patients performed poorly only during effortful tasks [15
]. A second reason for variable outcomes may be a speed-accuracy tradeoff in depressive patients as described by Kalb et al. [8
]. Thirdly, reduced performance may reflect low motivation to respond, i.e. poor ‘responsiveness’ [1
]. To minimize misinterpretations due to such confounding factors, auditory tests in depression should employ difficult tasks and monitor speed-accuracy tradeoff and responsiveness.
The present investigation applied pitch identification, pitch contour perception, and pitch discrimination tasks which reflected different auditory skills and neurophysiologic processes [10
]. The tests were adjusted to high task difficulty by selection of small pitch variations such that the tests were sensitive to impairments [10
]. To detect a potential speed-accuracy tradeoff, reaction times were recorded. Moreover, we considered the sum of correct and incorrect responses as measure of responsiveness.
Based on the quoted literature the hypothesis was tested, that auditory accuracy during pitch identification but not during pitch contour perception and pitch discrimination is impaired in depressive patients. This finding was expected to emerge independent of potential covariates, i.e. speed-accuracy tradeoff, responsiveness, motivation as well as sex, age, musical experience, education, and smoking.