INVESTIGATING STIMULUS SALIENCE AND PERCEPTUAL LOAD INTERACTION USING A HYBRID VISUAL-SEARCH FLANKER TASK A Mini-dissertation submitted in partial fulfilment of the requirements for the degree MA Research Psychology In the Department of Psychology at the UNIVERSITY OF PRETORIA FACULTY OF HUMANITIES By Gerrit Stefanus de Jager Supervisor: Ms Clare Schür Co-supervisor: Prof David Maree i Acknowledgments I would like to thank the following people (and cats): My wife for her support and for loving me despite the fact that I drive her crazy My cats Token, Botter, Kenny and Heidi for making me the world’s fastest “Control + s” presser. I’ll be on “Ripley’s Believe it or Not” one day thanks to them My parents for supporting my venture to become a psychologist even if it’s not a “real” job like being an accountant or a lawyer Clare Schür for acting as a critical soundboard for my silly ideas and always being supportive… even when I’m obviously wrong Prof David Maree for making me feel like I’m Jon Snow, and inspiring me to not be Jon Snow ii DECLARATION I, Gerrit Stefanus de Jager, hereby declare that this dissertation, to be submitted to the University of Pretoria for the degree Master in Research Psychology, is my own original work and has not been submitted to this University or any other tertiary institution for any degree. Signed: _______________________ This _______ day of ________ 2015 iii Summary The perceptual load theory of selective attention proposed by Tsal and Lavie (1994) and Lavie (1995) argues that selective attention is predominantly necessitated by perceptual capacity limitations. In order to account for the experimental evidence where stimuli are attentionally selected either early or late, Lavie (1995) proposed that early selection occurs when perceptual capacity has been reached, while late selection occurs when perceptual capacity has not been reached. This effect has been demonstrated with the use of hybrid visual-search flanker search tasks on numerous occasions (Lavie, 2004). However, some researchers argue that the selection of stimuli is attributable to salience and not to perceptual load. Due to the increased salience of flankers in low perceptual load trials the distractor identity is much more readily processed, thereby leading to the distractor interference. Lavie (1995) attributes the increased distractor interference in low perceptual load trails to the automatic allocation of spare perceptual resources; a process that is mediated by perceptual load levels. This study investigates the potential interaction between perceptual load and distractor salience by presenting 20 participants with a hybrid visual-search flanker task, but placing salient colour singletons distractors in half the trials. The results indicate that the compatibility effect is largely nullified in low perceptual load trials containing salient distractors. The non-salient distractor trials, however, produced a significant compatibility effect as predicted by the perceptual load theory of selective attention. The lack of a significant compatibility effect in salient distractor trials might be an indication that top-down attentional control mechanisms can capitalise on the task-irrelevant colour feature to suppress the processing or perception of the distractor. This finding problematises the hypothesis that the automatic spill-over of perceptual capacity is responsible for the distractor interference in low perceptual load trials as necessitated by perceptual load theory. iv Table of Contents List of Figures ................................................................................................................................ x List of Tables ................................................................................................................................ xi 1. Overview of the Study ................................................................................................................... 1 1.1 Introduction ............................................................................................................................. 1 1.2 Research problem .................................................................................................................... 5 1.3 Rationale. ................................................................................................................................ 6 1.4 Aims and Objectives ............................................................................................................... 7 1.5 Description of Methodology ................................................................................................... 7 1.6 Theoretical Framework ........................................................................................................... 8 1.7 Structure of the mini-dissertation ............................................................................................ 9 2. Literature Review ........................................................................................................................ 11 2.1 Brief overview of approaches to the study of attention ........................................................ 11 2.1.1 Attention as a limited capacity system ................................................................ 12 2.1.2 Alertness and arousal ........................................................................................... 14 2.1.3 Vigilance .............................................................................................................. 14 2.2 Selective Attention ................................................................................................................ 14 2.2.1 A fundamental sub-component of attention ........................................................ 15 2.2.1.1 Early selection theories ................................................................................ 16 2.2.1.2 Late selection theories ................................................................................. 18 2.2.1.3 Attenuation of stimuli .................................................................................. 19 2.2.1.4 A paradigmatic shifts in the study of attention ............................................ 20 2.3 The perceptual load theory of selective attention ................................................................. 21 2.3.1 Definition of perceptual load ............................................................................... 23 2.3.2 The experimental paradigm of the load theory of selective attention .................. 24 2.3.2.1 The visual search paradigm ......................................................................... 25 2.3.2.2 The filtering paradigm ................................................................................. 26 2.3.2.3 Hybrid visual-search flanker tasks ............................................................... 28 v 2.3.2.4 The effect of aging on selective attention .................................................... 30 2.4 Criticisms of perceptual load as a construct .......................................................................... 33 2.5 Top-down and bottom-up processing ................................................................................... 33 2.5.1 Evidence for bottom-up driven attention ............................................................. 35 2.5.2 Evidence for top-down driven attention .............................................................. 37 2.5.3 Bottom-up versus top-down debate and perceptual load theory.......................... 39 2.6 Alternative accounts of the effect of perceptual load on selective attention ......................... 40 2.6.1 Dilution account .................................................................................................. 41 2.6.2 Salience account of selective attention ................................................................ 44 2.7 Conclusion ............................................................................................................................ 49 3. Methodology ................................................................................................................................ 51 3.1 Introduction ........................................................................................................................... 51 3.2 Research question, aims and objectives ................................................................................ 52 3.2.1 Objectives and hypotheses................................................................................... 53 3.2.1.1 Hypothesis 1 ................................................................................................ 53 3.2.1.2 Hypothesis 2 ................................................................................................ 53 3.2.1.3 Hypothesis 3 ................................................................................................ 53 3.2.1.4 Hypothesis 4 ................................................................................................ 54 3.2.1.5 Hypothesis 5 ................................................................................................ 54 3.2.1.6 Hypothesis 6 ................................................................................................ 54 3.2.1.7 Hypothesis 7 ................................................................................................ 54 3.2.1.8 Hypothesis 8 ...............................................................................................