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Vigilance refers to the readiness to respond to a stimuli and it requires observer to maintain and remain alert to specified stimuli for prolonged periods of time. This study is designed to know acquisition and development of vigilance in children across different age groups and to understand vigilance performance differences across gender if any in the Indian context. In this study forty healthy children from four age groups (3-5; 5-7; 7-9; 9-11 years) completed a vigilance task for 15 minutes duration using cognispeed software. The data provided an opportunity to examine the developmental changes of performance on vigilance task and the effects of age and gender on the performance. The reported indexes included vigilance scores i.e., average recognition frequency (%) and mean reaction time (m sec) across age and gender. Results showed a significant increase in the vigilance scores as age increases and no significant gender differences. High vigilance scores were obtained for older children compared to younger children and decrease in the mean reaction time as age advances. This study provided an age specific distributions of the vigilance performance and are consistent with the hypothesis that cognitive inhibition develops during the primary school years. Further studies can be carried out to address how sustained attention/vigilance and language acquisition are related in children and; how it facilitates for language development.
Key words: Cognispeed, Attention, Reaction time, Age groups.
ACQUISITION OF VIGILANCE IN CHILDREN
Attention is a concentration of mental activity. It is the cognitive process of selectively concentrating on one aspect of the environment while ignoring the other things (James, 1980). Posner & Boies (1971) classified attention as selective attention, divided attention, focused attention and sustained attention/vigilance. All this plays a very important role in child language development. Sustained attention refers to the ability to maintain attention and alertness over time (Cicerone, 1997) and is typically equated with vigilance (Strauss, Thompson & Adams, 2000; Berardi, Parasuraman & Haxby, 2001).
Vigilance refers to the ability of an individual to maintain their focus of attention and to remain alert to stimuli over prolonged periods of time (Davies & Parasuraman, 1982; Parasuraman, 1986). The term 'vigilance' as applied to human behavior was coined by Head (1923), who referred to it as a state of maximum physiological and psychological readiness to react. The main characteristics of vigilance tasks are relatively long durations and the requirement to detect infrequent and unpredictable target stimuli against a background of other stimulus events. Vigilance paradigms have been used widely to assess the risk of performance deterioration in various work settings, as well as to examine and remediate attentional deficits in clinical populations (Nuechterlein, Parasuraman & Jiang, 1983).
Measurement of vigilance
Various tests and softwares were addressed in the literature to measure vigilance task. The most commonly used are: CogniSpeed software (Revonsuo & Portin, 1995), Conners Continuous Performance Test II (Conners & Staff, 2000), Vigil Continuous Performance Test (Cegalis, 1991), Vienna Test System: Vigilance (Schuhfried, 2007), The Digit Vigilance test (Lewis & Rennick, 1979) and The Gordon Diagnostic System (Gordon, 1983). Vigilance is measured in terms of aggregate performance (mean performance across the task), or in respect to a vigilance decrement (performance at the end of the vigilance relative to the beginning). In vigilance task of cognispeed software the subjects were assessed how vigilant they are for visual stimulus i.e., average recognition frequency and mean reaction time. Average recognition frequency is the average accurate response for entire 15 min task duration and responses were recorded in percentage. Reaction time is the elapsed time between the presentation of stimuli and subsequent response and responses were recorded in milliseconds.
Development of vigilance
In a review of 11 studies of age and vigilance, Davies & Parasuraman (1982) found that half of the studies reported evidence of an age effect on either hit rate (decrease with age), response time (increase with age) or false-alarm rate (increase with age). Parasuraman, Nestor & Greenwood (1989) using a more perceptually demanding task, found reduced hit rates and increased false-alarm rates in older adults. Overall, studies reported U-shaped function with a minimum at middle age for response time measures. Lin, Hsiao & Chen (1999) measured sustained attention using continuous performance test (CPT) and they examined the relationship between age and gender among 341 randomly selected school children between 6 to 15 years of age. They reported developmental changes and the effect of gender on the performance of CPT. The reason attributed for this developmental changes was inhibition processes. According to inhibitory processes, Bjorklund & Harnishfeger (1990) stated that younger children showed less efficient cognitive processing because their limited working memory space was consumed with irrelevant information mainly due to the immature inhibitory mechanism and this resulted in decreased performance in vigilance task (Bjorklund & Harnishfeger, 1990; Harnishfeger & Pope, 1996).
Factors affecting vigilance
They are many factors that affect vigilance. Some of them are event-rate effect, age, motivation, stress, cognitive aspects and habituation, sleep-wake systems. Stimulus exposure duration (display time) has been found to affect the subject's performance on vigilance tasks. Increase in display time may reduce vigilance decrements while decrease in display time may increase the vigilance decrements and reduce overall efficiency (Davies & Parasuraman, 1982). Another important factor considered while assessing vigilance in children was socioeconomic status. Levy & Hobbes (1979) studied the influence of social class and sex on vigilance in children. They found significant social class associations on a sample of 220 normal pre-school and primary school children.
Vigilance and language disorders
A considerable body of research has been focused on examining vigilance performance in language disordered population in both children and adults. Levy & Hobbes (1989) investigated a group of 51 male children (mean age of 9.1 years) for reading, phonetic spelling ability, vigilance and intellectual level. In their study, vigilance factor was significantly related to the diagnosis of moderate and severe attention deficit disorder with hyperactivity (ADHD). Similarly Leung, Leung & Tang (2000) measured vigilance in ADHD and control children. They concluded that children with ADHD performed worse than normal children, in that the former made more commission errors and had longer reaction times. Study by Michael, Klorman, Salzman, Borgstedt & Dainer (1981) clearly indicated that school age hyperactive children's ability to sustain attention on visual vigilance tasks was deficient when compared to that of control population. Tannock & Schachar (1996) stated that children with clinical attention deficits have a higher incidence of language impairments.
In 1974, Tarver & Hallahan in the review studies of distractibility, hyperactivity, impulsivity, vigilance and intersensory integration on attention deficit children with learning disabilities concluded that children with learning disabilities were deficient in their ability to maintain attention over prolonged periods of time. Swanson (1980, 1983) in a developmental study of vigilance reported that learning-disabled children made less correct detection and more false responses and less sensitive to critical stimuli than nondisabled children at all ages on vigilance task.
Studies were also carried out to know the relationship between sustain attention/vigilance and SLI. Finneran, Francis & Leonard (2009) assessed sustained attention using visual CPT in 13 children with SLI and 13 typically developing age-matched controls. They concluded that children with SLI had reduced capacity for sustained attention in the absence of clinically significant attention deficits that over time could contribute to language learning difficulties. Spaulding, Plante & Vance (2008) investigated sustained selective attention in children with SLI and no diagnosis of attention-deficit disorder as compared with typically developing age-matched peers. They reported significant group differences in accuracy in the degraded condition for the auditory stimuli such that the children with SLI performed less accurately than the age-matched control group. These findings suggest that children with SLI may have difficulties with sustained selective attention.
Adult language disorder cases like aphasia, right hemisphere damage and traumatic brain injury showed deficient in sustain attention or vigilance performance. According to studies by Wilkins, Shallice & McCarthy (1987) and; Rueckert & Grafman (1996) damage to the right hemisphere produced disproportionate deficits in a cluster of abilities variously termed alerting, arousal, vigilance or sustained attention. Laures (2005) studied reaction time and accuracy in individuals with aphasia during auditory vigilance tasks and findings indicated that the subjects with aphasia were less accurate during both tasks than the control group. Recently, Vijay (2007) measured vigilance in the age range of 30 to 80 years using cognispeed software. He found mean vigilance score of 76.33 % in the age range of 30 to 60 years and 37.77 % in the age range of 60 to 80 years. He concluded decreased vigilance performance as age advances.
The review of literature suggests an intricate relationship between vigilance performance, age and language disorders. The study of vigilance task provides a detailed index of the stability and the change in performance over time. Such changes may be related to communication success as well as success in other areas such as academic performance (Robin, Max, Stierwalt, Guenzer & Lindgren, 1999). Hence it is essential for a speech language pathologist to know the acquisition and developmental pattern for vigilance task from different age groups of children. There are many studies reported in the western literature about the vigilance performance in normal and disordered groups, but no attempt has been made to study vigilance across age groups in normal children in Indian context. Therefore this study was taken up. The main objective of the study was to know the acquisition and development of vigilance in children across different age groups and gender difference in vigilance performance in Indian context.
Forty healthy school going children (20 boys and 20 girls) in the age range of 3 to 11 years participated in the present study. Participants were divided into four age groups consisting of 10 subjects (5 boys and 5 girls) in each group. Group I participants were in the age range of 3 to 5 years with a mean age of 4.2 years. Participants of group II were in the age range of 5 to 7 years with a mean age of 6.1 years. Group III included participants in the age range of 7 to 9 years with a mean age of 8.4 years and Group IV participants were in the age range of 9 to 11 years with a mean age of 10.3 years.
All the participants attended an English medium primary school. They were native speakers of Kannada language (Dravidian language, spoken in the state of Karnataka). Participants were screened by a qualified speech language pathologist and who had no history of speech, language, cognition or visual impairment were included for the study.
Cognispeed is easy to use test software for measuring the speed and accuracy of human information processing, developed by Revonsuo & Portin (1995) at University of Turku, Finland. It contains ten separate tests which can be used to measure the attention function, working memory, automatic and controlled information processing. Cognispeed software was installed in Compaq Presario CQ-45 Laptop, running on Microsoft windows. For this study, vigilance performance was measured by selecting vigilance test in Cognispeed software set for 15 minutes duration with controlled presentation time and rate.
Selection of stimuli: The stimuli were single alphabet letters and the target letters selected were A, G and M. Target stimuli are those stimuli (letters) for which subject was asked to respond and for the same stimuli software will recognize as the genuine response.
Presentation of stimuli: Letters were presented at the center of the computer screen on gray square. The alphabet letters were presented randomly one by one at the centre of the square. In this study, the criteria was set at 30 %, the presentation time of each stimuli was set at 500 msec and interstimulus interval (ISI) between letters was set at 1000 msec. The test continued for duration of 15 minutes without interruption.
Instruction: Each child was instructed to pay attention only to target letters (A, G & M) presented at the centre of the gray square and to press the <space bar> as quickly as possible once he/she recognizes the target letter.
Test environment: Testing was carried out for each participant in silent room with minimal background noise. Participants were seated 60 cm away from the computer monitor.
Response: Participant task was to press the <space bar> key as early as possible when they identify the target stimuli presented in random order. The software measures the accurate recognized frequency out of the presented frequency called as average recognition frequency. The results of the test were presented in terms of five minute blocks and also in total duration. So the results compared accurate responses, change in the reaction time and in the number of the mistakes made during the first (0-5 minutes), the second (5-10 minutes) and the last five minutes (10-15 minutes). The average recognition frequency was represented in percentage and mean reaction time was represented in milliseconds.
The analyzed data was tabulated for four age groups of children and subjected to statistical analysis using SPSS (version 10). Average recognition frequency (%) and mean reaction time (m sec) was calculated in each group. Two way ANOVA was administered to note main effect for age and gender and; interaction effects of age and gender on average recognition frequency (%) and mean reaction time (m sec).
Average recognition frequency (%) across age groups and gender.
Table 1 and Figure 1 & 2, shows the mean and SD of average recognition frequency (%) for each age group across gender. Results revealed that increase in the vigilance scores as age increases with least score of 45.8 % (4.02) in group I followed by 55.2 % (7.49) in group II, and group III of 60.4% (5.14) and finally 73.7 % (4.40) in group IV with high scores. On treating the data with two way ANOVA, a significant main effect was obtained across age groups [F (2, 32) = 44.105, p < .001]. For further information, Boneferroni's pair wise comparison showed a significant difference (p<0.05) across age groups. However there was no significant difference found between group II and group III participants (p>0.05). And also, there was no significant main effect between gender [F (1, 32) = 0.185, p = 0.669] and interaction effect between age and gender [F (3, 32) = 0.987, p = 0.411] was noted.
Mean reaction time (m sec) across age groups and gender
Mean reaction time values in milli seconds for all the age groups across gender are represented in Table 1 and Figure 3 & 4. The mean reaction time for group I participants was 652.1 msec (40.02), in group II it was 640.4 msec (58.53), 579.3 msec (48.13) for group III participants and 506.4 msec (44.10) in group IV participants. Statistical analysis showed that there was a significant main effect across age groups [F (3, 32) = 18.237, p < .01]. All the age groups were compared using Boneferroni's pair wise comparisons adjustments. The results revealed statistical significant difference (p <0.05) except between group I and group II (p >0.05). Further, no significant main effect of gender [F (1, 32) = 0.511, p = 0.47] and interaction effect between age and gender [F (3, 32) = 0.528, p = 0.665] was observed.
Average recognition frequency (%)
The findings of the present study for average recognition frequency indicate that the vigilance performance increases with age especially in the age range of 3 to 11 years i.e., higher vigilance scores were noted for older children and lower scores for younger children and is consistent with the hypothesis that cognitive inhibition develops during the primary school years (Bjorklund & Harnishfeger, 1990). Harnishfeger (1995) defined cognitive inhibition as the process of actively suppressing previously activated cognitive contents or cognitive processes. The efficiency of cognitive inhibition was also hypothesized to change with age during childhood and hence lead to developmental changes on performance of neuropsychological tests like CPT and vigilance (Bjorklund & Harnishfeger, 1990; Harnishfeger & Pope, 1996). The results are also consistent with the findings of Parasuraman, Nestor & Greenwood (1989); Davies & Parasuraman (1982); Lin, Hsiao & Chen (1999) and Bjorklund & Harnishfeger (1990) where they reported higher vigilance scores in older children.
The reason attributed for significant lower vigilance scores for preschool children may be because they tend to attend the most salient characteristics of the stimulus, to position cues and to random items, whereas children between 5 to 7 years of age, scan a visual array more systematically, though scanning is still erratic might have affected the performance. However, higher vigilance scores in older children may be because of the ability to direct the attention towards a recognized goal. Hence, the scores were higher comparatively than other two previous groups in children around 8 years. Whereas, increased instrumental or instructional learning and more task relevant information recall capacity in older children between 10 to 14 years of age could be the reason for statistically significant higher vigilance scores than other groups (Hagen & Kail, 1975).
Further research is warranted to clarify the possible factors for gender differences in vigilance performance. Until then, gender of participants should not be ignored in interpreting the degraded vigilance performance. The results of the present study were consistent with the previous studies where older children perform better compare to younger ones and no gender differences in vigilance performance (Levy, 1980; Seidel & Joschko, 1990).
Mean reaction time (m sec)
Results clearly indicate that there is a decrease in the mean reaction time (m sec) as age increased. The results obtained are consistent with previous studies which report that reaction time is faster in older children compared to younger children (Jevas & Yan, 2001; Luchies, Schiffman, Richards, Thompson, Bazuin & DeYoung 2002; Hultsch, MacDonald & Dixon, 2002). The faster reaction time may be attributed to reduced speed of information processing among older children and hence the time taken for retrieving a letter decreased as age increased.
The present study results may also be discussed on lines of study by Welford (1980), who speculated on the reason for slowing reaction time with age. It is not just simple mechanical factors like the speed of nervous conduction. It may be the tendency of older children to be more careful and monitor their responses more thoroughly. When troubled by a distraction, younger children tend to devote their exclusive attention to one stimulus, and ignore another stimulus, more completely than older children (Redfern, Muller, Jennings & Furman, 2002).
The current study investigated development of vigilance in normal school going children in the age range of 3 to 11 years. Results clearly indicated that there was a significant increase in the vigilance score and reduction in the reaction time as age increases, supporting the hypothesis that cognitive inhibition develops during the primary school years (Bjorklund & Harnishfeger, 1990). Similar results were reported in studies on vigilance scores and reaction time (Davies & Parasuraman, 1982; Bunce, Barrowclough & Morris, 1996; Giambra, 1997; Parasuraman et al, 1989, 1991; Jevas & Yan, 2001; Luchies et al 2002; Hultsch et al 2002). To conclude, sustained attention/vigilance has been found to be a crucial, and in many respects a prerequisite skill for scholastic achievement (Robin et al 1999). The ability to sustain attention underlies basic process of perception and learning. When this ability is impaired, learning and academic performance are affected (Levy & Hobbes, 1989; Tarver & Hallahan, 1974; Swanson, 1980; 1983). The data from the present study is helpful to give a more comprehensive view of the sustained attention/vigilance skills of normal children in different age groups. Further studies can be carried out to address how sustained attention/vigilance and language acquisition are related in children and; how it facilitates for language development.