Perceptualand Motor Skills, 1991, 72, 617-618.
O Perceptual and Motor Skills 1991
SPATIAL SUSTAINED ATTENTION: BETTER FOCUSED THAN DIVIDED? ' PATRIZIA S. BISIACCHI AND MAD0 A. PROVERB10 Universi~degli Studi di Padova Summary.-Visuospatial attention was studied using three different reaction time tasks in a sustained attention paracbgm (N = 35). Contrasting with findings from a phasic attention paradigm, our results suggest an equal ability to divide or focus sustained attention in the left and right fields m s~mpleRT, a Go/No go-task, and choice RT.
An influential model of visual attention (2) states that there are two modes of attending to visual displays. I n the first mode, attentional resources can be allocated simultaneously over several spatial locations, while in the second, they can be focused to only one spatial location at a time. Several experiments (1, 3) have shown that to concentrate attention on only one point of visual display (focused attention) is better than to allocate attentional resources across an entire display (diffuse attention). The implication is that, whereas the amount of resources can be equally distributed among different locations, there is a disproportionate share of these resources in focused attention. I t follows that reaction times (RTs) in conditions of focused attention are expected to be faster than RTs obtained when attention is divided, because the attentional resources are limited. The present experiment was designed to investigate further these two processing modes when task requirements are different. Thirty-five subjects (16 men and 19 women) were randomly assigned to one of three experimental tasks (simple RTs, Go/No go, choice RTs). All subjects were right-handed according to an handedness questionnaire (4). Subjects were instructed to fixate the center of the screen and to respond as quickly as possible to the stimulus onset (a luminous square of 1" of visual angle appearing at 6.5" of eccentricity) by pressing a telegraph key with the index finger of the left or the right hand. At the beginning of each of three blocks, subjects were told to maintain attention to the center, the right or the left hemifield (in the sustained attention paradigm). Two blocks required selective attention to the right or the left hemifield (in the covert orienting paradigm). The other block required diffuse attention: subjects paid attention to the center and responded to stimuli in each hemifield. According to which experimental task the subjects were assigned, they had to respond in one case to every stimulus presented (simple RTs, Task I),
'Correspondence may be addressed to l? Bisiacchi and M Pmverbio, Dipartimento di Psicologia, Piazza Capitaniato 3, 35139 Padova, Italia.
P. S. BISIACCHI
M. A. PROVERB10
only to the left or the right stimulus in the focused condition, and to both stimuli in diffuse condition (GolNo go, Task 2); to both stimuli but using the compatible hand (choice RTs, Task 3). A personal computer was used to control stimulus presentation and R T measurements. RTs faster than 140 msec. and slower than 500 msec. were excluded from analysis I n each block 200 stimuli were presented at random in the left or the rlghc visual field. After 50 stimuli a short pause permitted the subjects to relax. The order of various blocks and of the hand used for the response were balanced across subjects. A preliminary analysis of sex differences showed no systematic effect of sex on these experimental tasks so data were combined in other analyses. TABLE 1 MEANRTS AND STANDARD DEVIATIONSFORTI-IREE TASKSBY ATTENTIONAND VISUALFIELD Task
Focused Attention Left Field Right Field
Diffuse Attenr~on Left Field h g h t Field M SD M SD
A three-way analysis of variance (task x field x attention) was applied to mean RTs (see the table) for the attended stimuli. No significant effect was found, indicating no difference between focused and diffuse attention. In other words, when the attention is directed to the center of the visual field and a response is required for both spatial locations, subjects are as fast as when they have to focus attention in one spatial location. O n e possible explanation is that subjects can diffuse attention over the entire visual field without decreased processing efficiency, which is not simply dividing available attentional resources. REFERENCES 1. CASTIELLO, U., & UMLT~,C. A. Size of the attentional focus and efficiency of processing. Acta Psicologica, 1990, 73, 195-209. 2. J O N ~ E S J., Further toward a model of the mind's eye's movement. Bulletin of the Psychonomic Socieiy, 1983, 21, 247-250. COHEN,Y.,CHOATE,L. S., HOCKEY,R., & MAYLOR,E. Sustained concen3. POSNER,M. I., tration: passive filtering or active orienting? In S. Kornblum & J. Requin (Eds.), Preparatory states and processes. Hillsdale, NJ: Erlbaum, 1984. Pp. 49-65. 4. SALMASO, D., & LONGONI, A. M. Pmblems in the assessment of hand preference. Cortex, 1985, 21, 533-549.
Accepted March 22, 1991.