Fig 1.
Examples of the morph steps for two face exemplars.
Numbers indicate proportion of happiness expressed by the face: 0 corresponds to 100% sad, 1 to 100% happy, and 0.5 to 100% neutral. The middle position (0.56) is a slightly happy expression of 12% (see text).
Fig 2.
Negative perceptual bias in patients with MDD.
Patients with MDD recognized facial expression as happy if a higher proportion of happiness is expressed by the face compared to HC. MDD = major depressive disorder; HC = healthy controls (A): Example of a fitted logistic function to the behavioral responses for one representative participant. Intensity of the affective expression is displayed on the y-axis. Transition from sad to happy corresponds to values between 0 and 1 on the x-axis. 0 corresponds to the fully sad expression, 1 is attributed to a happy expression. A y-value of 1 corresponds to a classification of the face as happy in each trial and a y-value of 0 to the response ‘sad’ in each trial, 0.5 is assigned if a face is equally often classified as happy and sad. The x-value indicates the PSE of the curve corresponding to the criterion for the categorical shift. The categorical shift from sad to happy indicates the morphed facial expression that is equally often categorized as happy and sad. (B): Bar plot, displaying the mean PSE at T1 for both groups. *p = 0.025. Error bars denote within-subject standard errors of mean [53].
Table 1.
Demographic data.
Fig 3.
Perceptual bias is reduced in patients with MDD with diminished depressive symptoms.
MDD = major depressive disorder; HC = healthy controls. Bar plots depicting mean PSEs (A) and slopes (B) of the logistic functions for the two groups and two time points. A significant interaction of time and group was observed for the PSE, indicating the inflection point of the logistic functions (p < 0.001). For the slopes of the logistic functions, indicating the abruptness of the categorical shift from sad to happy, no main effects or interactions were found. *: interaction of time and group, p < 0.001. Error bars denote within-subject standard errors of mean [53].
Fig 4.
Correlation between change of depressive symptoms and change of perceptual bias in patients with MDD.
For patients diagnosed with depression, the change in the degree of severity of depressive symptoms between the two time points of testing correlated positively with the change of the perceptual biases between the two sessions. The severity of depressive symptoms is indexed by BDI scores. The perceptual bias is indicated by the PSE of the individual logistic functions.
Fig 5.
Suppression time modulation by sad and happy faces at T1.
Bar plots depict suppression time modulations for happy and sad facial expressions relative to neutral expressions for patients with major depressive disorder (MDD) and healthy participants (HC) at T1. Values > 1, represented by the dotted line, indicate longer suppression times in relation to neutral faces. No differences between emotions or groups were found. Error bars indicate within-subject standard-errors of the mean [53] MDD = major depressive disorder; HC = healthy controls.