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Chapter 7

Chapter 7 True Experiments II

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University of Toronto Scarborough
Connie Boudens

Chapter 7 True Experiments II  Factorial designs- disentangle both direct and interactive influences on measured responses o Involves just one variable o More realistic o More efficient  Multifactorial for experiments that vary two or more independent variables and provide direct tests of the main effects of each independent variable as well as the interaction effects between and among the independent variables MUTLIFACTORIAL DESIGNS  Single-factor experiment, a researcher can always add a new level to an existing independent variable, as for example when a baseline, no-treatment group is incorporated into the study design  Multifactorial experiment, an altogether new independent variable is devised and incorporated into the research design  Lowe, Hirsh, and Anderson illustrates a multifactorial design with two independent variables  Exhibit 7.1, there are two independent variables: mood induction, with two levels, happy or sad, and cognitive exercise, also with two levels, verbal or visual o Two independent variables—mood induction and cognitive exercises—are qualitatively different with two levels o Induce a positive mood, participants listen to a jazzed-up version of Bach’s Brandenberg Concerto No. 3 (played by Hubert Lewis), and for a sad mood, they listen y
 to Prokofiev’s Alexander Nevsky’s Russia under the Mongolian Yoke played at halfspeed o Other independent variable, participants perform a verbal exercise of generating remote word associations and a visual exercise of detecting and selecting targets presented on a computer monitor o Idea behind the study: how emotion (mood induction) might influence thinking (cognitive exercises) and whether a particular mood state might be better for performing a particular cognitive exercise  Exhibit 7.1 (Multifactorial design- between subjects) – need four groups of research participants, each randomly assigned to one of the four experimental conditions: (1) happy mood/verbal; (2) happy mood/visual; (3) sad mood/verbal; and (4) sad mood/visual o Happy mood induction followed by the verbal task; happy mood induction followed by the visual task; sad mood induction followed by the verbal task; sad mood induction followed by the visual task  Exhibit 7.1 (Multifactorial design- within subjects) – all participants would be run through each of the four experimental conditions o Happy mood induction followed by the verbal task and then the visual task and the sad mood induction followed by the verbal task and then the visual task  Advantages to a multifactorial research design: more realistic, economical and efficient design to evaluate and to test the separate and joint influences of one or more independent variables on a dependent variable NOTATIONS AND TERMS  Simplest multifactorial experimental design contains two independent variables, each with two levels or values  Factorial experiments are typically designated or identified by a numbering notation o 2x2 factorial design has two independent variables, with two levels or values  Number of numbers- number of factors or independent variables; Number values- how many levels of the independent variables o 3x4 factorial design indicates two independent variables, one with three levels, and the other with four levels  Order of the numbers makes no difference (could be identified as 4x3)  Every level of each independent variable is combined; three levels of one independent variable are combined with the four levels of the other independent variable for a total of 12 levels or treatments o The number of treatment groups that we have in any factorial design can be calculated by simply multiplying through the number notation  2x2 example, we have 2x2 = 4 groups THEORY AND EXPERIMENTATION  Theory guides how an experiment is designed, how independent variables are developed and manipulated, how dependent variables are measured and what specific hypotheses are tested A COMPLEX WITHIN-SUBJECTS EXPERIMENT  Reginald B. Adams and Robert E. - eye-gaze direction and facial expressions are important in conveying social information  Eye-gaze direction and facial expressions can each be understood in terms of approach-avoidance motivation o Share informational value as signals of approach, propelling behavior forward, setting the stage for direct expression, confrontation or ―fight;‖ conversely, they may fuel avoidance, triggering inhibition, culminating in ―flight‖ from negative stimuli, of potential danger and threat  Adams and Kleck constructed a theory, which proposes that facial expressions of emotions and gaze direction operate as a social signaling system that governs our basic evolved behavioral tendencies for approach or avoidance o Our fluency in perceiving facial expressions of emotions reflects a dynamic interaction of signals associated with gaze direction and affective displays etched on our visages DECODING FACIAL EXPRESSSIONS OF EMOTION  Facial expressions are nonetheless complex stimuli, configurations of more basic elementary features  n   Larger size of fearful eye whites in comparison to that of happy eye whites  Whalen and colleagues recorded neural activity while participants viewed a series of slides, each with either fearful white eyes or happy white eyes o Bund the amygdala of the human brain to be especially sensitive to fearful white eyes but not to happy white eyes DEVISING INDEPENDENT VARIABLES  Adams and Kleck formulated a two-prong hypothesis: o Anger faces with direct gaze would
 be more readily perceived than anger faces with averted gaze o Fear faces with averted gaze would be more readily perceived than fear faces with direct gaze  Test their hypothesis: first create experimental stimuli to construct facial stimuli that varied in expression and gaze direction o Used Adobe Photoshop to doctor gaze direction of faces of anger and fear o They created four types of faces: (1) anger with direct gaze, (2) anger with averted gaze, (3) fear with direct gaze, and (4) fear with averted gaze o Organize their four types of faces into an experimental task for participants to perform o Participants view one at a time on a computer monitor a face that had an expression of either anger or fear and a gaze direction of either direct or averted o Participants made a speedy judgment as to whether the face displayed anger or fear by responding via a right or left mouse click o Used within-subjects design which allowed for the comparison of participants’ response times in emotional judgment for the four different kinds of faces THE 2X2 DESIGN Table 7.1 shows the four combinations: (1) direct gaze/anger (A 1B1), (2) averted gaze/anger (A2B1), (3) direct gaze/ fear (A1B2), and (4) averted gaze/fear (A2B2)  Upper left cell=Mean response time to correctly judge faces displaying anger expressions with direct gaze (mean = 862.3)  Upper right cell = Mean response time to correctly judge faces displaying anger expressions with averted gaze (mean = 914.1)  Bottom left cell= Mean response time to correctly judge faces displaying fear expressions with direct gaze (mean = 944.5)  Bottom right cell = Mean response time to correctly judge faces displaying fear expressions with averted gaze (mean = 891.2)  Effect of type of facial expression on response time can be examined by looking at the rows MAIN EFFECTS  Effects of each independent variable on a dependent variable are referred to as the main effect of the independent variable  Main effect can be calculated for each independent variable INTERACTIONS  A statistical interaction occurs when the effects of one level of the independent variable depend on the particular level of the other independent variable  Example: Table 7.1 – Direct gaze decreased response time in judging anger faces, averted gaze reduced response time in judging fear faces but increased response time in judging anger faces o Pattern reflects an interaction between type of emotional expression depended on gaze direction of the face o Describe the interaction as: On one hand, direct gaze led to faster judgment of anger faces but slower judgment of fear faces. On the other hand, averted gaze led to faster judgment of fear faces but slower judgment of anger faces INTERPRETING RESULTS OF MULTIFACTORIAL DESIGNS  RECALL: Factorial designs provide two distinct sources of information: (1) main effect of each independent variable by itself and (2) any interaction effect of the independent variables  Main effects are statistically independent of interaction effects o Can have no significant main effects but still have significant interaction effects or vice versa  An interaction indicates that any interpretation of a main effect of an independent variable by itself will be misleading o Bec
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