Elsevier

Brain and Cognition

Volume 71, Issue 1, October 2009, Pages 9-13
Brain and Cognition

Sustained attention to local and global target features is different: Performance and tympanic membrane temperature

https://doi.org/10.1016/j.bandc.2009.03.001Get rights and content

Abstract

Vision researchers have investigated the differences between global and local feature perception. No one has, however, examined the role of global and local feature discrimination in sustained attention tasks. In this experiment participants performed a sustained attention task requiring either global or local letter target discriminations or watched the same displays without any work imperative. Reaction time to targets was slower when global feature discriminations were required than when local feature discriminations were required. Tympanic membrane temperature (TMT) was utilized in this study as an index of cerebral activation. Participants in the global letter detection condition had elevated post-task right TMT, indicative of reduced cerebral activation in the right hemisphere, in comparison to participants in the local letter detection or no-work imperative conditions. Both the performance and physiological results of this study indicate increased cognitive fatigue when global feature discriminations are required.

Introduction

People and other animals are often required to monitor the environment for prolonged periods of time while attempting to detect infrequently occurring critical events and to ignore more frequently occurring noncritical events. This phenomenon is labeled vigilance or sustained attention (Nuechterlein et al., 1983, Warm, 1984). In many real world scenarios a person’s ability to sustain attention plays a crucial role. In the scientist’s laboratory vigilance tasks are useful for exploring and understanding the control of attention and the nature of attention deficits (Manly et al., 1999, Robertson et al., 1997). Despite a long history of research, vigilance researchers have overlooked an important issue influencing vigilance: whether the critical target is discriminated with global or local features. Visual objects are hierarchically organized with a global form being composed of smaller local forms or features. Psychologists have investigated global–local feature detection, for example, using global–local letter stimuli, letters composed of smaller letters (see Fig. 1 for examples) (Navon, 1977). Global discriminations are generally easier and quicker for people to make than local discriminations (Kimichi, 1992, Lux et al., 2004), although this advantage depends on the configuration of the local–global stimuli and the context in which the discrimination are made, the stimulus set (Kinchla and Wolfe, 1979, Lamb and Robertson, 1990).

The role of global and local feature discrimination has not been examined previously in the context of sustained attention. In most global–local feature detection studies there is an external prompt (cue) before figure presentation which serves both as a memory aid, reminding the participant which feature to detect, and a general arousal aid, reminding the participant to pay attention in general. The participants in these studies are not required to self sustain their attention to the task of feature discrimination.

There are reasons to suspect vigilance may benefit from a task requiring local feature discrimination. First, the executive control of vigilance has been found to be right hemisphere dominant in right-handed people using a variety of brain imaging techniques (Duschek and Schandry, 2003, Helton et al., 2007, Hitchcock et al., 2003, Stroobant and Vingerhoets, 2000). Recent studies indicate, moreover, that the decline in vigilance performance, the vigilance decrement, is accompanied by a parallel decline in right cerebral blood flow velocity (CBFV) from pre-task baseline levels (Hitchcock et al., 2003, Schnittger et al., 1997). Indeed Hitchcock et al. (2003) demonstrated that the absolute decline in right hemisphere CBFV in vigilance tasks is positively related to the psychophysical and cognitive demands placed upon observers: higher task demand leads to greater decline in right hemisphere CBFV. Second, global discrimination of stimuli has been found to be right hemisphere dominant, whereas, local discrimination of stimuli has been found to be left hemisphere dominant (Lux et al., 2004, Yamaguchi et al., 2000). Third, current models of attention propose a division of labor among separate though connected neural systems for pattern recognition and sustained attention (Posner & Peterson, 1990). The maintenance of focused attention and initial target recognition during prolonged target detection tasks requires the integrated activity of separate neural sub-systems.

The two hemispheres of the brain are separate, though networked information processing resources, with tasks being shared or partitioned by the hemispheres to improve overall processing (Kinsbourne, 1982, Kinsbourne and Hicks, 1978). Global letter discriminations requiring sustained effort and vigilance may place heavy demand on the right cerebral hemisphere, as both vigilance and global pattern recognition seem to be right lateralized. As Kinsbourne (1982, p. 413) elegantly stated, “When concurrent acts involve connected territories, they interfere with each other. When they are represented at a distance from each other in functional cerebral space, they interfere little and the capacity of the human operator appears correspondingly enhanced.” Therefore there may be an enhancement of performance in vigilance tasks requiring local level discriminations, as they share the burden across the hemispheres more effectively than sustained global feature detection tasks.

The alternative perspective of a sustained attention performance advantage for global as opposed to local target discriminations cannot, however, be ruled out a priori. The right hemisphere, being both more adept at global feature discrimination and sustaining attention, may be advantaged by hemispheric task integration.

Participants in the current study performed either a global or a local target detection task for 20 min. In addition to observed differences in performance, we were interested in using a relatively under utilized physiological marker of lateralized cerebral activation, tympanic membrane temperature (TMT), to support our hypothesis. Researchers examining tasks known to be cerebrally lateralized have demonstrated reliable lateralized TMT results in both humans and chimpanzees (Cherbuin and Brinkman, 2004, Cherbuin and Brinkman, 2007, Helton et al., in press, Hopkins and Fowler, 1998, Meiners and Dabbs, 1977). Researchers using TMT have found that increases in TMT correspond to decreases in cerebral activation and decreases in TMT correspond to increases in cerebral activation (Cherbuin and Brinkman, 2004, Cherbuin and Brinkman, 2007, Hopkins and Fowler, 1998, Meiners and Dabbs, 1977). Cortical temperature is highly correlated with TMT in the ipsilateral ear (Mariak et al., 2003, Schuman et al., 1999). Carotid blood flow is correlated with cerebral blood flow, r = .7 and changes in cerebral activity alters carotid blood flow (Chu et al., 2000). Tympanic membrane blood perfusion is influenced by carotid blood flow. The head cools as carotid blood flow increases due to increased blood exchange with the rest of the body and increased heat radiation near the surface of the neck and head. This cooling affects both the tympanic membrane and the brain, as both are warmed from inside the head and are relatively insulated (Sukstanskii & Yablonskiy, 2006). Indeed, Sugino and colleagues (1997) found a relationship between TMT and cerebral blood flow (CBF) estimated by stable xenon-enhanced computer tomography: elevated TMT is indicative of reduced CBF and lowered TMT is indicative of increased CBF. In the present study we investigated lateral TMT differences following global and local sustained target detection tasks and a no-work control, where participants merely view the displays, as well as performance differences between the global and local vigilance tasks.

In summary, in accordance with Kinsbourne’s (1982) theory of hemispheric interference, we predicted a performance advantage in a local as opposed to global feature discrimination vigilance task. In addition, we predicted an elevation of right TMT after performing the global feature vigilance task as compared to the elevation of right TMT after performing the local feature vigilance task or no-work control. Elevated right TMT is indicative of greater decline in right CBFV. Therefore, a relative elevation of right TMT in the global task, which we predicted is more challenging than the local task, would be in accordance with Hitchcock et al.’s (2003) previous finding that there is a greater decline in right CBFV for more demanding vigilance tasks.

Section snippets

Participants

Fifty-one undergraduate students (27 men and 24 women) served as participants. All of the participants had normal or corrected-to-normal vision and were right-handed as indexed by the Edinburgh Handedness Inventory (Oldfield, 1971). Participants ranged in age between 18 and 33 years (M = 20.4 years, SD = 2.7) and were recruited from Michigan Technological University’s participant pool.

Procedure

The 51 participants were assigned at random to one of the three conditions: global vigil, local vigil or control

Performance

Because the overall rate of correct detections was high (M = 97.17%) and the false alarm rate low (M = 0.37%) for the vigilance tasks in this experiment, reaction time was chosen as the appropriate performance metric. Mean reaction times of responses were calculated for each participant for each period of watch in ms. Shapiro–Wilk tests for normality were performed on the mean reaction times and indicated deviation from normality, p < .05. Therefore mean reaction times were log10 transformed as

Discussion

Reaction time to targets was faster in the local than the global discrimination vigilance task. Because both sustained attention and global letter discrimination are right lateralized, we hypothesized that this combined information processing demand on the right hemisphere would lead to impaired performance in the global vigilance task in comparison to the local vigilance task. In the local target task, the processing load is shared more efficiently across the hemispheres. This result is in

Acknowledgment

This work was supported by the Department of Defense University Research Instrumentation Program (DURIP) administered by the Air Force Office of Scientific Research (FA-9550-07-1-0500), W.S. Helton Principal Investigator. The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Department of the Air Force, Department of Defense, or the US government. We would like to thank Willard Larkin for providing administrative

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