Human aging, which is characterized by a series of changes in cognitive processes involving a multidimensional attention change process, has become an important focus in aging research. There is increasing evidence that different functions of human attention are served by separable neural networks (Fan et al., 2002, 2005; MacDonald et al., 2000; Parasuraman et al., 2001; Posner & Petersen, 1990). The alerting network functions to maintain vigilance and respond to incoming information in areas of the frontal cortex and in parietal areas of the dorsal visual pathway (Marzo et al., 2014; Petersen & Posner, 2012). The orienting network involves selective allocation of attention to stimuli in priority processing environments, and is associated with the temporo-parietal junction, frontal eye fields, and superior parietal cortex (Fan et al., 2002, 2005). The executive network is responsible for information selection during complex tasks, resolution of conflict between competing cognitive processes, and coordination involved in process transformation, in which some areas of the prefrontal cortex and anterior cingulate cortex play a key role (Fan et al., 2002, 2005; Funahashi & Andreau, 2013).

To investigate age-related effects researchers have typically used the Attention Network Test (ANT), which measures each attention network and their interactions at the same time (Fan et al., 2002, 2005, 2007; Posner & Rothbart, 2007). Several studies have reported that orienting network efficiency does not decrease as people age because older adults can use spatial cues effectively (Fernandez-Duque & Black, 2006; Gamboz et al., 2010; Jennings et al., 2007). Although both orienting and executive effects are equivalent in young and older adults, there is evidence that alerting is significantly reduced in older adults (Gamboz et al., 2010). Jennings et al. (2007) also found that alerting is significantly reduced in older adults, before and after overall speed has been taken into account (see also Festa-Martino et al., 2004). In contrast, other researchers have reported age-related enhancement of the alerting network, such that older adults benefit from a change toward a liberal response criterion brought about by the alerting cue (Fernandez-Duque & Black, 2006). Regarding the executive network, several previous studies have shown that this function is not impaired by age (Fernandez-Duque & Black, 2006; Jennings et al., 2007), whereas others have shown there is an age-related decline (Mahoney et al., 2010).

These inconsistent ANT results for the effects of aging may be partially attributed to the number of experimental trials that participants completed. For example, in Gamboz et al.’s (2010) study there were three blocks of 96 trials, whereas in Fernandez-Duque and Black’s (2006) study all possible combinations among flankers and cue types were represented in five blocks, each comprising 48 trials. A greater number of experimental trials could increase cognitive fatigue in older adults, which would affect their performance. Therefore, if previous researchers based their analysis on only a few blocks of the task, they may not have been comparing network effects that accurately represent the two age groups. Thus, we aimed to determine whether aging has an impact on each attentional network, focusing specifically on the alerting and executive networks. Because of the inconsistent nature of previous results, we considered it vital to also account for the number of experimental trials as an influencing factor.

Method

Participants

Participants were 38 young adults and 36 older adults. Young adults comprised 18 women and 20 men (M_age = 21.35 years, SD = 1.8, range = 19–25), who were recruited from South China University of Technology. Older adults comprised 18 women and 18 men (M_age = 72.17 years, SD = 2.9, range = 68–80), who were recruited from the senior college in Guangzhou, China. Participants who had a history of neurological and psychiatric disorders and were receiving psychoactive drug therapy that could change cognitive ability, and older adults who scored less than 26 on Mini Mental State Tests (Folstein et al., 1975) were excluded. All participants had normal or corrected-to-normal vision and normal hearing. The study was approved by the Ethics Committee of South China University of Technology, and participants gave their written informed consent and were paid for their participation (USD 15.00).

Procedure

Stimuli consisted of a row of five horizontal black lines, with arrowheads pointing to the left or right, according to the ANT paradigm (Fan et al., 2002). On a gray background, the target was an arrow at the center pointing either left or right. There were three congruency conditions for the arrows presented to each side of the target: two arrows pointing in the same direction as the target arrow was the congruent condition, two arrows pointing in the opposite direction from the target arrow was the incongruent condition, and straight lines without arrow heads was the neutral condition. A single arrow or line consisted of 0.55° of visual angle and the contours of adjacent arrows or lines were separated by 0.06° of visual angle. The stimuli consisted of 3.08° of visual angle.

As shown in Figure 1, at the beginning of each trial there was a fixation cross presented in the center of the screen, with a variable interval of 400 to 1,600 ms. Then, a center cue, a double cue, a spatial cue, or no cue was presented for 100 ms. After 400 ms of cue offset, a target display appeared and remained on the screen until the participant reacted, or if there was no response the target was removed after 1,700 ms. The fixation cross was then displayed for 3,500 ms, and then the next trial began (Fan et al., 2002). Participants were asked to press the left or right mouse button as quickly and accurately as possible to indicate the direction of the target arrow. Each participant completed two blocks with 96 trials in each, and each block lasted approximately 8 minutes, with a short break of about 2 minutes between blocks. Before beginning the test, each participant practiced with a training block of 32 trials.

Data Analysis

We excluded the less than 2% of reaction times that were more than two standard deviations above or below the mean in each condition. We then computed the results for each attentional network (Fan et al., 2005) based on the proposed ANT measures, as follows: Executive network = reaction time to targets with incongruent arrows minus targets with congruent arrows. Orienting network = reaction time to targets with central cue minus targets with spatial cue. Alerting network = reaction time to targets with no cue minus targets with double cue. We used these data to conduct a two-way mixed model analysis of variance with block (Block 1 vs. Block 2) as the within-subjects factor and age group (young adult vs. older adult) as the between-subjects factor for each attentional network. Using the Greenhouse–Geisser epsilon correction factor, we corrected the degrees of freedom.

Results

As shown in Table 1, older adults exhibited slower response times (761 ms) than did young adults (483 ms; p < .001), but the accuracy rates for each group were similar (young adults, 97.6%; older adults, 97.9%; p > .10). Results for the three attentional networks in both age groups are shown in Figure 2.

For the alerting network, the main effect of block (33 and 44 for Blocks 1 and 2, respectively) was not significant across groups (p = .095), the difference according to age group was significant (young adults = 49.5, older adults = 28.5; p < .03), and the block × age group interaction was not significant, F < 1.

For the orienting network, no significant effects were found (ps > .10) for block, age group, and block × age group effects.

For the executive network, the main effects of block, age group, and block × age group were significant (ps < .01). Further, although there was no significant difference in executive network function according to age group in Block 1 (77.5 for older adults, 88.5 for young adults; p = .548), the difference was significant in Block 2 (−46.8 for older adults, 56.7 for young adults; p < .01), and the main effect of block was significant for older adults (p < .01) but not for young adults (p = .147).

Discussion

We investigated the effects of aging on the alerting, orienting, and executive functions of human attention using the ANT. Although older (vs. young) adults exhibited a slower overall response, the three attentional functions showed different modulations according to age group and block of trials. For the alerting function the value was larger for young adults, regardless of the block of trials. For the executive function there was no significant age difference between the performance of older and young adults in Block 1, but the value was lower for older adults in Block 2. Finally, neither age nor trial block had a significant effect on the orienting function. Thus, there was a dysfunction in the alerting function of older adults in both blocks of trials, and in the executive function of older adults in the second block, whereas there were no age group differences for the orienting function.

Across the two blocks of the ANT paradigm, the longer reaction time for the alerting function in the older adults is consistent with previous findings (Gamboz et al., 2010; Jennings et al., 2007). Decreased cortical levels of noradrenaline may cause a decline in the alerting function (Ferrari & Magri, 2008; Lohr & Jeste, 1988; Oberlin et al., 2005), and the reduction of the attention resources of older adults has been attributed to this (Craik & Byrd, 1982; Mahoney et al., 2010). In contrast, previous researchers have shown that the alerting function is generally not impaired as people age (Rabbitt, 1984), or that there is age-related enhancement (Fernandez-Duque & Black, 2006). These inconsistent findings may be attributable to the number of experimental trials that were used.

Consistent with our finding of no age-related effects on the orienting function, previous results also show that the efficiency of the orienting network is not affected as people age because older and young adults can use spatial cues equally as effectively: Fernandez-Duque and Black’s (2006) participants’ M_age = 72.5 years; Gamboz et al.’s (2010) participants’ M_age = 67.9 years; Jennings et al.’s (2007) participants’ M_age = 61–87 years. These findings indicate that both young and older adults benefit from physical or symbolic cues that direct attention to the possible location or identity of upcoming target information (Kramer & Strayer, 2001).

Previous studies have shown that aging has an important impact on cognitive response speed, that is, executive control processes like task switching, dual tasking, and inhibition all significantly decrease with age (Reimers & Maylor, 2005; Salthouse et al., 1996; Turner & Spreng, 2012). The most relevant finding related to executive function is that people aged over 60 years exhibit a decrease in the inhibition of irrelevant information, which is usually accounted for by the frontal lobe hypothesis of aging (De Troyer et al., 1994). However, similar to our results regarding no significant effect of aging on executive function, previous researchers have not found any indication of a general age-related decline of executive function (Fernandez-Duque & Black, 2006; Jennings et al., 2007). Hence, the frontal lobe hypothesis of aging has been challenged on the basis of several considerations, including general slowing down, dependence on the specific task, control processing, and the effects of sensory degradation (Ben-David & Schneider, 2009; Turner & Spreng, 2012).

We find it interesting that our results show there was a significant difference in executive function in the second block of trials, with young adults performing better than older adults. This dysfunction could result from an increase in cognitive fatigue (i.e., after the task of Block 1) and an insufficient decision processing capacity in people aged over 70 years (Holtzer et al., 2011; participants’ M_age = 80.6 years), which needs further investigation. In addition, aged-related sensory perceptual changes could be another source for the superior performance of young (vs. older) adults on the ANT. In addition to declines in the cognitive abilities of memory and recognition, older adults often have low-level visual impairment, including decreased visual acuity, spatial vision, and spatial contrast sensitivity (Craik & McDowd, 1987; Spear, 1993). The decline in performance on the ANT by older adults could be due to these impaired visual functions. It is also possible that the use of larger images of the arrows in the ANT, for example, would have changed our results. This issue also needs further investigation.

In sum, although older (vs. young) adults exhibited a slower overall response time, the results for the orienting function were the same. In contrast, the results for the alerting function significantly declined across the older adults’ task performance, whereas the dysfunction in their executive function was evident, with their longer performance resulting from cognitive fatigue. Future researchers could seek to further clarify the specificity of attention function using ANT with people aged over 70 years, as it is an important issue with significant implications for health in the context of aging and in clinical settings. This will enhance understanding of attention disturbances in people aged over 70 years, and how to address these disturbances.

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This research was supported by the Humanity and Social Science Youth Foundation of the Chinese Ministry of Education (19YJC860007) and the 2019 Project of the 13th Five-Year Plan for the Development of Philosophy and Social Sciences in Guangzhou (2019GZQN06).

Guoming Yu, School of Journalism and Communication, Beijing Normal University, 19 Xinjiekouwai Street, Haidian, Beijing 100875, People’s Republic of China. Email: [email protected], or Lun Zhao, School of Educational Science, Liaocheng University, No. 1, Hunan Road, Dongchangfu, Liaocheng, Shandong 252059, People’s Republic of China. Email: [email protected]