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Chapter 7

Chapter 7 Notes 97-03.doc

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University of Toronto Scarborough
David Nussbaum

PSYB01 Chapter 7 – True Experiments II - Factorial designs: complex experimental designs - Multifactorial designs: experiments that vary two or more independent variables Multifactorial designs - Adding a new level in research design is different than adding another independent variable - E.g. Mood Induction and Cognitive Tests by Rowe, Hirsh and Anderson (2007) o 2 Independent variables: Mood Induction and Cognitive Exercises,  2 levels for Mood induction: Happy and Sad  2 levels for Cognitive Exercises: Verbal and Visual o 4 groups of participants required: Happy and Verbal, Happy and Visual, Sad and Verbal, Sad and Visual o For within-subjects: All participants would have to go through all 4 situations - More realistic, more economical with efficient design to evaluate separate and joint examples - Results will show how the independent variables interact - Notation and Terms o Factorial experiments are typically designated or identified by a numbering notation (e.g. 2x2 Factorial design has two independent variables with two levels or values) o The resulting number also tells how many combinations there are as treatment groups A Complex Within-Subjects Experiment - Perceived Gaze Direction and the Processing of Facial Displays (Reginald B. Adams and Robert E. Kleck) o According to their theory, eye-gaze direction and facial expressions can each be understood in terms of approach-avoidance motivation (Approach: Confrontation or “fight”, Avoidance: Inhibition or “flight”) PSYB01 Chapter 7 – True Experiments II o Adams and Kleck propose that facial expressions of emotions and gaze direction operate as a social signaling system that governs our basic evolved behavioural tendancies for approach or avoidance - Decoding Facial Expressions of Emotion o Whalen compares “eye whites” of happy and fearful participants (more in fear). Found that amygdala of human brain was sensitive to fearful white eyes but not to happy eyes - Devising Independent Variables o Two aspects of face that would be important for emotional expression  Facial muscle contractions that form different emotional expressions such as anger and fear  Gaze direction such as direct or averted eyes o Developed hypothesis  Anger faces with direct gaze would be more readily perceived than anger faces with averted faces  Fear faces with averted gaze would be more readily perceived than direct gaze o Experimental stimuli: construct facial stimuli that varied in expression and gaze direction  Anger with direct gaze, anger with averted gaze, fear with direct gaze, fear with averted gaze (made with Adobe, based on Ekman’s faces) o Experimental task: task constructed for participants to perform  Participants had to make judgement about faces with right or left mouse click o Within-subjects design chosen because each person is held as own control (some people may just respond faster in general, etc.)  Second advantage is that it is more economical - The 2x2 Design o The dependent measure was response time in milliseconds for judging faces as expressions of either anger or fear PSYB01 Chapter 7 – True Experiments II o Column means show the average of response time for direct gazes in general (by averaging columns) (row means = same thing) - Main Effects o Main effect: effects of one independent variable on a dependent variable are averaged over all levels of another independent variable o Because the means for direct and averted gaze were nearly identical, we conclude that gaze direction does not significantly influence response time o Participants responded faster to angry faces - Interactions o Interactions: when one independent variable depends on another independent variable o Effect of emotional expression depended on gaze direction (direct gaze helped identify angry faces and averted gazes slowed it, opposite for fear faces) - Interpreting Results of Multifactorial Designs o Factorial designs provide 2 sources of info  Main effect  Interaction o Always identify interaction first before main effect because main effect could depend on level of other independent variable o Simple main effect: compares the influence of one level of an independent variable at a given level of another independent variable o Cross-over interaction: where effects of one independent variable on a dependent variable are reversed at different levels of other independent variable (2x2 designs) o If there were no interactions, the two lines would be parallel - The 2x2 Logic o There would be 8 possible outcomes of the 2x2 design  No effect of eye gaze
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