Dark Side of Attention: Unnoticed or Forgotten?
The phenomenon of failing to detect a stimulus in plain sight when attention is engaged elsewhere is called inattentional blindness (IB; Simon & Chabris, 1999). According to Simon and Chabris, IB can be explained as a perceptual deficit not due to vision defects. This is supported by the finding that 46% of subjects fail to notice unexpected salient events in selective-looking tasks (eg. failure to notice a man in a gorilla suit walking across the screen). Accordingly, IB is a perceptual deficit that depends on not only goal-directed cognitive control, but also on perceptual load or potentially task-relevant information. In a second approach to IB, Wolfe (1999) proposed that IB can be explained by deficits in memory, where individuals perceive stimuli, however briefly, but immediately forget they had seen it. Deficits in memory or Inattentional Amnesia (IA) is supported by research in working memory capacity (WMC) where WMC is a primary candidate predictor for IB. Before 2014, it was not possible to distinguish empirically between memory deficits and perceptual deficits for IB because there was no holistic test that distinguished between never seeing an object and seeing an object and immediately forgetting about it. Currently, there are researchers who have demonstrated that IB reflects a failure of perception by measuring the level of IB among participants who look for unexpected and expected events in moment-by-moment conscious perception tasks (Ward & Scholl, 2014). Therefore, the purpose of this article is to examine attention and IB, to indicate age-related changes in attention that contribute to IB, to review the research on the two approaches that explain IB (memory or perceptual deficits), and finally, to end the debate on which of the two approaches more appropriately explain IB.
To better understand the inattention phenomenon, it is important to first understand what attention is. Attention requires a certain amount of selection where certain signals in the environment are selected and others are ignored. All measures of attention require selection because there is too much sensory information (perceptual load) in the environment for all of it to be processed at once. Attention is selection with or without awareness. Automatic or inattentional selection is selection without awareness that is triggered by certain stimuli in the environment and is innately specified (do not need to be learned). In contrast, control or intentional attention is selection with awareness where only one controlled process can be conducted at a time. These endogenous selection processes are carried out with specific goals that reflect individual’s specific knowledge and strategies for a certain situation. Understanding how controlled or endogenous selection contributes to missing irrelevant stimuli will be important to identify the factors that lead to IB. Some of these factors may be indicative of age-related or developmental changes in attention and are more evident in certain modes of selection.
The ability to deploy attention flexibly improves with age. There are more age-related changes in endogenous modes of selection (controlled processes) than there are in exogenous modes of selection (automatic/innately specified processes). The reason for this developmental difference is because the areas of the brain (prefrontal cortex) in the automatic modes are among the last to develop and the first to deteriorate with age. Therefore, earlier developmental differences are driven primarily by biological factors and so processes that involve automatic selection, like reflex, will show the least change in age whereas controlled selection, like in exploration, will show the greatest variability (Enns & Trick, 2006). Although attention is a process that improves with age, endogenous or controlled processes of selection decline with age and are more sensitive to developmental periods across the lifespan. Therefore, age-related changes in controlled selection may be playing a role in perceptual deficits that lead to inattentional blindness.
Inattentional or perceptual blindness is the process in which individuals fail to recognize an unexpected stimulus that is in plain sight when their attention is focused on something else. About 50% of participants consistently fail to notice an unexpected stimuli when they are engaged in a specific task (Simon & Chabris, 1999). Researchers use reaction time measures or feature based measures (what type of stimulus it is; is it more easily detected than others?) under sustained and dynamic conditions to measure IB. The level of inattentional blindness may be explained by the saliency of the stimulus. Most et al. (2000) support this in their study where they suggest that IB may be more pronounced depending on the spatial location or orientation of the stimulus. Consistent with these findings, focused selective attention depends on goal-directed cognitive control and on the perceptual load of a given task. Therefore, inattentional blindness can be attributed to a variety of external and internal factors.
Findings have indicated that age-related changes across the lifespan are factors that contribute to IB. For example, attentional capacity increases with age, where awareness increases with development due to the enhanced capacity. These findings reveal that IB is greater in younger children and greater perceptual load is associated with greater IB in children but not adults. These results indicate that age-related changes for attentional capacity may play a role in the development of IB among children. This is consistent with findings where children are less able than adults to filter out distractors. In contrast, Stroop studies indicate that younger children are susceptible to greater interference than older children and adults. However, children more prone to distraction may be accounted for by their greater ability to focus on a given task, compared to adults. Therefore, executive attention control processes may be the source of individual differences among different age groups as age-related improvements in visual selective attention and resistance to distraction develops with maturation.
The second approach to inattentional blindness can be explained by deficits in memory, rather than deficits in perception. According to Wolfe, individuals may be phenomenally aware of missed events, but inattention may somehow prevent it from encoding into memory. This phenomenon yields a form of inattentional inaccessibility or inattentional amnesia (IA). According to O’Shea and Fieo (2014), individual differences in memory, executive functioning, and age-related cognitive changes predict the occurrence rate of inattentional amnesia in adulthood. Working memory capacity (WMC) may be playing an important role in predicting inattention as a source of mnemonic deficits. Additionally, age-sensitive cognitive abilities, such as memory, may predict inattentional blindness. This is demonstrated in studies that find that age-related changes in the prefrontal cortex and declines in executive control influence performance on different memory tasks. Consequently, specific memory processes, such as with memory retrieval, are associated with prefrontal cortex atrophy and executive function impairments in late adulthood. Therefore, anterior brain region development and maturation may contribute to mnemonic deficits which are associated with greater incidences of IB in older adults, compared to performances on IB in children with healthy executive working memory loads. Unfortunately, research between age-related changes in working memory and inattentional amnesia or IB, is scarce. The problem with measuring IA is that if participants are asked about their perception of unexpected events after the fact, then it may be too late (Ward & Scholl, 2014). Because there are no holistic tests that distinguish between events that are not seen and events that are forgotten, research findings on predictive factors of IB, such as with executive processes of attention, will be examined instead.
As mentioned previously, executive control processes have been found to decline with age. Recently, researchers have been able to interpret executive function (EF) development changes by determining neural correlates within structural imaging studies (using MRIs). Brain development, consisting of progressive and regressive changes (myelination, maturation), is an important predictor of later executive function. In fact, EF continues to strengthen significantly throughout childhood and adolescence. However, there is then a decline in EF starting as early as young adulthood. Therefore, although WMC has been a candidate predictor for IB, inattentional blindness may also be sensitive to developmental changes in EF across the lifespan, especially since aging increases susceptibility to inattentional blindness.
Differences in executive control of attention rather than differences in WMC can account for the variance observed in working memory tasks predictive of IB. This is supported in findings where participants engaged in attention demanding tasks have regions in the prefrontal cortex that are activated. As we learned in high school, the prefrontal cortex is a part of the brain that is involved in higher-order mental ability. Therefore, it is possible that executive control of attention is predictive of IB since the prefrontal cortex is an important source for executive processes. Reaction times are used as a measure of IB and they are strongly correlated with processing speed. This begs to question whether using reaction time measures for processing speed is appropriate to predict IB. Additionally, there is greater variability and greater increase in reaction times among older adults compared to younger adults. This is consistent with the age-related changes in executive control of attention among children and adults that account for IB. However, further research is warranted to investigate the relation between WMC, processing speed, and executive control processes that predict inattentional blindness. Lastly, there are no holistic tests that validate measures of executive functions, especially since the components of these functions are unknown. Furthermore, because attentional task performances vary between different age groups, a greater variety of measures, that include attentional and executive functions that reflect attention in all its developmental stages, is required.
In a recent study, Ward and Scholl (2014) explain IB as a perceptual deficit by controlling for perceptual decay over time (memory), as evidenced from repeated failures of awareness. The researchers employed sustained inattentional blindness tasks where 100 participants viewed moving black and white shapes on a display and counted how many times the shapes crossed the display’s midline. The participants also had to report whether they had noticed an unexpected event (a gray cross appearing and traversing the entire screen) after the task was completed. The second group included 100 participants who had to identify the unexpected event immediately after seeing it. The researchers increased the saliency of the unexpected event by changing the cross to a dark red or dark blue. They also increased the speed at which the letters were moving, increasing the difficulty of the task (consequently increasing the salience of the unexpected event). Furthermore, participants in this group had the explicit task to immediately respond to anything unexpected after the trial, even if they did not see anything. The results indicate that inattentional blindness persists even when the observers are asked to report the unexpected event during online perception, with no time for perceptual decay whatsoever. The researchers demonstrate that IB reflects a failure of perception, not of subsequent memory where the unexpected event occurs multiple times, consequently reflecting a genuine deficit in moment-by-moment conscious perception. Furthermore, a strength of Ward and Scholl’s study is that the researchers make the unexpected event more salient. Consistent with other findings, it would be unlikely that participants would notice a very salient event (such as a very colorful letter or a man in a gorilla suit) and then immediately forget about it. In fact, participants who fail to notice the gorilla suit consistently report being surprised when they are shown what they miss. Therefore, is unlikely that inattentional blindness can be explained by deficits in memory. The only permissible approach is that IB can only be explained by perceptual deficits.
One of the implications for inattentional blindness explained by perceptual deficits is that IB can affect real-world tasks, like automobile driving. This is not to be confused with distraction and driving. When drivers are talking through a Bluetooth device or texting while looking at the road, they are receiving two sources of information. Some adolescents have developed the motor coordination and memory skills needed to text without looking at their cellphones. While the driver is focusing attention on the device, they might be blind to the actual road. Although the behavior may seem automatic and habituated in a controlled environment, the two sources of information when driving can contribute to failing to notice an unexpected event. Additionally, the developmental trend is that younger children are less able than adults to filter out distractors in their environment. Moreover, children who get their licences later on are at less risk of getting into accidents and have less risky-driving behaviors, such as texting and driving. Therefore, inattentional blindness can be better explained as a perceptual deficit when taking into account accidents that involve texting and driving, especially when drivers have developed the habit in texting without looking at their devices. This last point opens a discussion as to how safe BlueTooth devices are. Although the driver may be looking at the road, if their attention is engaged elsewhere (i.e., focusing on the conversation using the BlueTooth device), they may be blind to unexpected events on the road.
Another implication for IB as a perceptual deficit is that offenders may be finding ways to waive their responsibility and lesson their sentences because their acts are justifiable by deficits in cognitive functioning. The ongoing debate discusses whether inattentional blindness should equate to criminal negligence because attention deficits can be avoidable, or whether crimes are justifiable because IB is, by default, a deficit in cognitive functioning that is beyond the control of the driver. The rationality of criminal negligence is that it allows the justice system to deal with the problem where the problem remains unsolved. So, giving a crime a cause or fault (IB) removes the responsibility of the offender and removes criminal negligent charges. Cognitive psychologists and researchers should use caution when defining IB and addressing its predictors. Although inattentional blindness should be explained by perceptual deficits, IB is a controlled and endogenous process so crimes should not be justified by these deficits. Researchers should emphasize that inattentional blindness is a controlled process that results from perceptual deficits when individuals are engaged in a task. Therefore, using the driving examples, drivers have control over which events they are focused on. Any deviation away from perceptual awareness or attention-engaging behaviors could result in inattentional blindness and these instances of IB should be considered as negligent.
To conclude, inattentional blindness is explained by two approaches. The first is that IB is a perceptual deficit, characterized by unawareness of certain events in the environment when attention is engaged elsewhere. The second is that IB is a memory deficit, characterized by initially perceiving the event, but then immediately forgetting about it. The research findings on the difference between the two approaches is limited. According to most empirical studies, IB is better explained by moment-by-moment perceptual deficits rather than a function of time or perceptual decay (memory). This is further supported by findings that indicate greater prefrontal cortex activity, which is a source of executive processes, in participants who perform in IB tasks. In contrast, literature in mnemonic deficits that are predictive of IB is controversial. Some findings suggest a relation between speed processing, working memory capacity, general fluid intelligence, and inattentional blindness while others suggest WMC does not account for the variances observed in working memory tasks predictive of IB. Literature on working memory capacity is limited and research on inattentional amnesia warrants further investigation. Therefore, the only existing and sufficing empirical approach is the approach that explains IB as a deficit in perception, not memory.
References
Enns, J.T., & Trick, L.M. (2006). A framework for studying age-related change and individual variation in selective attention. In E. Bialystok & F. Craik (Eds.), Lifespan cognition: mechanisms of change (pp. 43-56). NY: Oxford University Press.
O’Shea, D.M., & Fieo, R.A. (2014). Individual differences in fluid intelligence predicts inattentional blindness in a sample of older adults: A preliminary study. Psychological Research, 2, 513-523. doi: 10.1007/s00426-014-0594-0.
Simons, D.J., & Chabris, C.F. (1999). Gorillas in our midst: Sustained inattentional blindness for dynamic events. Journal of Perception, 28, 1059-1074. doi: 10.1068/p2952.
Ward, E.J., & Scholl, B.J. (in press). Inattentional blindness reflects limitations on perception, not memory: Evidence from repeated failures of awareness. Psychonomic Bulletin & Review. Retrieved from http://www.yale.edu/perception/Brian/bjs-pubs.html
Wolfe, J.M. (1999). Inattentional amnesia. In V. Coltheart (Ed.), Fleeting memories: Cognition of brief visual stimuli (pp.71-94). MA: MIT Press.
