Post_Stim_Results

Animate/inanimate face recognition task was administered using the Presentation program (Neurobehavioral Systems). Face stimuli were obtained from Looser & Wheatley (2010) who morphed twenty inanimate faces with well-matched photographs of human faces using FantaMorph software (Version 3; Abrosoft Co., Beijing, China). The resulting image sets were the product of linear interpolation between the two (human/mannequin) original images. This kept the increments of physical change consistent across the morphing continuum, which consisted of 5 ‘human’ faces (1-5, containing 60-100% human aspects) and 5 ‘mannequin’ faces (7-11, containing 60-100% mannequin aspects) and a sixth, middle face that was considered a 50% human-50% mannequin version.This task consisted of the presentation of 9 blocks of faces presented on a different 15” laptop screen, placed at about eye level approximately 66 cm in front of participants. Each face stimulus block contained a sequence of 11 human-like faces morphed as previously described. This provided a total of 99 faces. When instructed to begin, participants saw a randomly selected face in the middle of the screen, (W: 10-12 cm; H: 11-15 cm) followed by a question as to whether the face was inanimate (1) or animate (2). Each trial lasted 3000ms (1000 ms face stimuli duration and 2000 ms response screen duration). Participants were instructed to relax and minimize movements since EEG was being recorded simultaneously.Presentation of faces was immediately followed by a question as to whether the face was inanimate (1) or animate (2). Reaction times (RTs) were collected for those responses. Outlier analysis of the data was performed in which RTs more than two standard deviations above or below the mean were removed. Participant responses were also analyzed by using polynomial regression fitting to compute the functions representing subjects’ responses. This was done by collecting and analyzing response data from individual subjects across the 9 face blocks (Cheetham & Jancke, 2013), each of which was shown to participants before and after stimulation. Each of the 9 face blocks contained 11 different morph images with a unique morph identifier, also known as a face continua. Response data for each face continua were aggregated and averaged, generating 9 functions displaying the response data prior to stimulation and 9 functions following stimulation. In pooling the 18 different polynomial curves, four cumulative functions were generated -- one for pre-STIM, post-STIM, pre-SHAM, and post-SHAM, thus allowing larger inferences on how participants responded to each morph image prior to and following the onset of stimulation to be drawn. Once the four cumulative functions were generated, the point of subjective equality (PSE) was calculated. This is the point at which a face was equally likely to be deemed animate or inanimate (following Looser & Wheatley, 2010). It was done by finding the polynomial function associated with the fitted curve and finding the x-coordinate corresponding to the point at which the function reached the 50% recognition point.