Shifts of Visual Attention: An Historical and Methodological Overview

Abstract An historical overview of the study of visual attention shifts is prese nted. Contemporary research on this problem is outlined and models of attention shift mechanisms are briefly described. In addition, several methodological variables are described that warrant consideration when evaluating claims about shifts of visual attention.Our ability to shift visual attention is apparent whenever we direct our eyes to ward one object while attending to something else at a different location. This is commonly ref erred to as using our "peripheral vision" and we do so, for example, when driving a car and keepin g our eyes on the road while attending to the sidewalks where pedestrians and children might a ppear. Undoubtedly, humans have been aware of this capacity for a good deal of our spec ies' history but tools were not available to study this phenomenon scientifically until the 1 9th century. Helmholtz found that he could voluntarily shift the focus of his attention to id entify groups of letters before he had sufficient time to execute an eye movement to those letter s (see Warren & Warren, 1968). He demonstrated this by illuminating the display of letters with a spark. The brevity of the illumination precluded eye movements because they usually require approximately 220 ms for execution (Fischer & Weber, 1993). When Helmholtz kept his attention on a pinhole at the centre of the display where his eyes remained fixated, he could identify only those letters in the immediate area. On the other hand, when he voluntarily decided to attend to the letters at a different location and shifted his attention in advance of the spark, he co uld identify only those letters in the attended area. Thus, with the advent of technology for pro ducing electrical sparks, voluntary shifts of attention made independently of eye movements were f irst studied in the laboratory.Later in the 19th century, James (1890) described attention shifts as being under voluntary or involuntary control. Others conducting experiments around this time demonstr ated that visual attention can be captured by the sudden onset of a stimulus (e.g., Titchener, 19 10). This work provided a framework for understanding one of the fundamental aspects of attenti onal control - shifts can be made in a goal - driven or in a stimulus - driven manner. Resear chers have referred to goal - driven shifts as endogenous, voluntary, or intrinsic; and to stimulus - driven shifts as exogenous, reflexive, or extrinsic. Goal - driven attention shifts are initiated voluntarily on the basis of a computational goal (e.g., shift attention to the location indi cated by the arrow cue presented in the centre of the visual field). Stimulus - driven shifts are i nitiated reflexively in response to abrupt - onset stimuli or visual transients somewhere in the visu al field (Yantis & Jonides, 1984; Yantis & Gibson, 1994, this issue). The distinction between th ese two types of control will be discussed in more detail later in the article.Very little research on attention was conducted during the behaviourist era in the first half of the 20th century until the pioneering work on auditory filtering by Broadbent (1952, 1958) and Cherry (1953). The evolution of visual attention research, as is usually th e case with any scientific endeavour, was influenced by technological advances. In particular, just as the independence of attention shifts and eye fixation was not studied scientifically until the equipment required to ignite electrical sparks was developed, so it was that thi s phenomenon was not studied in more detail until the 1970s when eye movement monitoring technolo gy was refined. Before this time, attention shifts could be studied only in the spirit of Helmholtz through the use of time - limited displays that were masked before eye movements could be made (i.e., displays with exposure durations less than 200 ms). Another technique used regularly during the past 30 years to study the dyna mics of visual attention shifts is location cueing. …