Introduction

Change blindness is a phenomenon where people fail to spot even large changes in a scene, when changes occur during a visual disruption [1,2] (Rensink et al., 1997; Simons & Levins, 1997). This effect occurs because we do not retain a full representation of all visual details in our environment from one moment to the next, so attention towards an item is necessary to detect a change in it [3,4] (Rensink, 2000; Rensink et al, 2000). Since the environment contains too much information to process at any one moment, attention allows us to attend selectively to the most important items and to devote less attention to information of less interest.

Autism spectrum conditions (ASC) are characterized by social and communication difficulties, alongside unusually narrow interests and repetitive behaviour [5] (American Psychiatric Association, 2013). Repetitive behaviours in ASC include resistance to change and a need for sameness, where even the smallest changes in the environment or routine may lead to a tantrum until the change is undone to restore the environment to its original state [6,7,8](Baron-Cohen, 2006; Kanner, 1943; Volkmar et al., 2005). The heightened perception of changes to local details in ASC is consistent with experiments reporting atypical sensory processing [9] (Tavassoli et al, 2014), and reports of enhanced visual perception in some [10,11] (Ashwin et al., 2009; Latham et al., 2013) but not all studies [12] (Tavassoli et al., 2011). Enhanced sensory processing may emerge from an imbalance in excitatory and inhibitory cortical activity in ASC [13,14] (Rubenstein & Merzenich, 2003; Vattikuti & Chow, 2010) and/or a steeper gradient of attention [15,16,17] (Robertson et al., 2013a,b,c), which may reflect lower levels of the neurotransmitter GABA [18] (Robertson et al., 2016).

A number of theories emphasize enhanced perception of detail as a central feature of ASC [19,20,21,22,23] (Baron-Cohen et al., 2009; Frith, 2003; Happe, 1999; Mottron et al., 2006; Plaisted et al., 2006), supported by research showing superior performance in ASC compared to controls on the Block Design task [24] (Shah & Frith, 1993), the Embedded Figures Test [25,26] (Jolliffe & Baron-Cohen, 1997; Shah & Frith, 1983), and visual search tasks [27] (Plaisted et al., 1998). These tasks involve the analysis of a shape in terms of its constituent parts, with greater feature detection in ASC attributed to differences in lateral inhibition during visual perception leading to sharper spatial attention [15,16,17] (Robertson et al., 2013a,b,c).

Despite this strong evidence for enhanced attention to detail in ASC, there have been mixed findings regarding the detection of change. One study of change detection in children with and without ASC reported no group differences in the ability to detect changes in objects [28] (Burack et al., 2009). Studies of change blindness have similarly failed to show convincing support for heightened attention to changes in ASC. In fact, a number of studies have reported greater change blindness in ASC compared to controls [29,30,31,32] (Fletcher-Watson et al., 2006; Fletcher-Watson et al., 2008; Kikuchi et al., 2009; New et al., 2010), which is inconsistent with theories of enhanced perception of details in ASC. Other change blindness studies have found no differences overall between adults with and without ASC [33] (Loth et al., 2008). In contrast, Smith and Milne [34] (2008) reported reduced change blindness effects in adolescents with ASC using short films where participants had to detect errors of continuity, with group differences being more apparent for items of marginal interest. A similar finding was reported for children with ASC who showed faster detection of changes in images of everyday life than controls, with the effect once again being most evident for items of marginal interest [35] (Fletcher-Watson et al., 2012).

One potential explanation for the mixed findings to date in change detection experiments in people with ASC compared to controls is the differences in methodology used across the studies. In particular, differences in the responses required by participants may have affected previous results in those with ASC, who have difficulties in aspects of executive function (EF) [36,37] (Ozonoff, 1995; Ozonoff et al., 1991). Previous research in change detection using more complex response methods requiring participants to press different buttons throughout the experiment have reported greater change blindness compared to controls [29] (Fletcher-Watson et al., 2006), while another change detection study using the same types of stimuli but with a simpler response involving the participant pressing just one button whenever they detected a change, reported reduced change blindness compared to controls which was particularly evident for changes to items of marginal interest [35] (Fletcher-Watson et al., 2012). However, reduced change blindness using the same types of static images and simple response requirement has not been reported to date in adults with ASC.

The aim of the present study was to investigate the detection of changes to items of central and marginal interest in scenes of everyday life in adults with and without ASC. Based on psychological models of enhanced local perception in ASC we predicted the ASC group would show reduced change blindness versus controls. Furthermore, based on previous reports and evidence for greater attention to items that others find insignificant, we also hypothesized that group differences in change detection would be particularly evident for marginal interest items.

Materials and methods

Results

There were no significant differences between the groups for age, t(42) = 0.58, p = .59, or for full-scale IQ, t(42) = 0.38, p = .70. The results of the AQ scores for the sample with ASC (mean AQ score = 38.2, SD = 6.0) included 88.0% of them scoring at or above the cut-off of 32, which is indicative of a diagnosis of ASC (Baron-Cohen et al., 2001).These scores were very similar to findings from previously published studies using the AQ with ASC samples [39] (Baron-Cohen et al., 2001) with a mean AQ score of 35.8 (SD = 6.5) and 80% of the sample scoring at or above the cut-off score of 32.

Response latencies

The statistics on response latencies for the detected changes revealed there was no main effect of Group, F(1, 42) = 1.85, p = .18, , showing no group differences overall in responses latencies to detect changes. However, there was a main effect of Interest Type, F(1, 42) = 275.1, p < .000, , with participants in both groups detecting the central interest changes quicker than marginal interest changes (Fig 1). This revealed that both groups showed a change blindness effect similar to previous studies.

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Fig 1. Response latencies for central and marginal interest changes.

Mean response latencies and standard errors for both groups to detect changes in central and marginal interest conditions. The ASC group was significantly faster than the control group to detect changes to marginal interest items, with no group differences for changes to central interest items.

https://doi.org/10.1371/journal.pone.0185120.g001

Importantly, there was an interaction between Group and Interest Type, F(1, 42) = 5.1, p = .03, . Post hoc independent samples t-tests showed there was no difference in response latency to detect Central interest changes for the ASC versus control group, t(42) = 0.36, p = .97. However the ASC group was significantly faster in detecting Marginal interest changes than the control group, t(42) = 2.8, p = .008 (Fig 1). Since there was a group difference in Detection Rates for changes of location, a further ANOVA was run without including the response latencies for location changes, and results still showed faster response latencies for the ASC group compared to the control group for detecting Marginal interest changes.

There was also a main effect of Type of Change, F(2, 41) = 19.03, p < .000, . Post hoc t-tests showed that a change in colour was detected faster than in both a change in location (p < .000) and a change in absence/presence, (p = .001), while no differences were found for response latencies to location compared to absence/presence changes (p = .10) (Fig 2).

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Fig 2. Response latencies for central and marginal interest changes.

Mean response latencies and standard errors by both groups for each of the three categories of changes. The ASC group was significantly faster than the control group to detect changes of location, with no group differences to detect changes of colour or absence/presence.

https://doi.org/10.1371/journal.pone.0185120.g002

There was an interaction between Group and Type of Change, F(2, 41) = 3.92, p = .044, . Post hoc independent-samples t-tests between groups showed that there were no differences for changes in colour, t(42) = 0.81, p = .42, or absence/presence, t(42) = 0.88, p = .38, but that the ASC group had faster response latencies than controls to detect changes in location t(42) = 2.5, p = .018 (Fig 2). There was no interaction found between Interest Type, Type of Change, and Group, F(2, 41) = 0.11, p = .84, .

Discussion

The present findings reveal differences in change blindness in adults with ASC compared to controls. On the one hand, the ASC group showed faster detection of changes to items of marginal interest by adults with ASC compared to control adults, demonstrating reduced change blindness for changes to items within scenes that are typically of lower salience. On the other hand, the ASC group detected approximately one fewer change in location compared to controls of within the marginal interest item changes, although the groups did not differ overall in the number of changes they detected and all participants performed quite well in the task (both groups at 90%+ detection rate). Together, the results demonstrate that people with autism attend to the world in a different way compared to controls, particularly towards items in scenes that are typically of less interest to others.

The present results are consistent with greater attention to small changes in the environment in people with ASC, as the detection of changes in change blindness paradigms requires attention to be focused on the location of the change (Simons & Rensink, 2005). Similar findings for reduced change blindness to marginal interest items in children and adolescents with ASC have been reported using images of scenes and short films [34,35] (Fletcher-Watson et al., 2012; Smith & Milne, 2008). Numerous clinical and anecdotal reports emphasize a local processing bias in ASC and a focus on small details around them that often appear insignificant to others [34,44,45,46] (Baron-Cohen, 2003; Cléry et al., 2013b; Fein et al., 1979; Smith & Milne, 2008). The enhanced sensitivity to changes may help explain the tantrums seen in children with ASC resulting from even small changes in their environment, with insistence on sameness being a central feature of ASC. If people with ASC have heightened awareness of small changes, this may overload sensory and perceptual processing resources and cause over-arousal [34,47,48] (Belmonte, 2000; Belmonte & Yurgelun-Todd Smith & Milne, 2008). The resistance to change and repetitive behavior seen in ASC might be adaptive, to help reduce the excess sensory and perceptual processing and the resulting arousal in ASC from small changes in their surroundings.

The finding of attenuated change blindness in ASC are also consistent with models and research showing enhanced perception of details alongside reduced processing of the context [19–26] (Baron-Cohen et al., 2009; Frith, 2003; Happe, 1999; Jolliffe & Baron-Cohen, 1997; Mottron et al., 2006; Plaisted et al., 1998; Plaisted et al., 2006; Shah & Frith, 1993; Shah & Frith, 1983). One recent study found children with ASC are faster on visual search tasks than typical children, and further showing to be as fast as typical adults [49] (Hagmann et al., 2016). The greater ability by those with ASC to detect certain changes in the present study is even more remarkable considering the task required all participants to intentionally look for a change between the images. The present results are in-line with other findings of reduced change blindness to marginal items in children and adolescents with ASC [34,35] (Fletcher-Watson et al., 2012; Smith & Milne, 2008), and extend these findings to include adults with ASC.

The detection of change relies on focused attention to the changing item, and people with ASC are said to have more focused attention compared to controls [50–52] (Lovaas & Schreibman, 1971; Lovaas et al, 1971; Rincover & Ducharme, 1987). An attentional focus with a sharper gradient around it was recently demonstrated in ASC compared to controls [15] (Robertson et al., 2013a). An overly focused attention may enhance change detection by allocating attentional resources to discrete locations, which facilitates the processing of details within the focus and produces less interference from distracting items around it. Greater attention to the marginal interest changes may also be due to a greater perceptual capacity compared to controls. Enhanced perceptual capacity has been demonstrated in ASC using response-competition paradigms and visual detection tasks [53,54] (Remington et al., 2009; Remington et al., 2012), and is thought to underlie findings of reduced inattentional blindness in ASC [55] (Swettenham et al., 2014). It is proposed that greater perceptual capacity is related to change blindness findings [55] (Swettenham et al., 2014). When change blindness conditions involve a low load, with load referring to the perceptual requirements of a task, then group differences are less likely to be found according to this view because both groups have adequate perceptual resources available. But under conditions of high load the ASC group demonstrates better ability to detect changes because they have more perceptual resources available to them than controls. Since detecting changes to the central interest items is easier than those to marginal interest items, this view predicts that the groups should not differ in the ability to detect central interest changes and that the ASC group should perform better than controls in detecting the marginal interest changes, which was what was found in the present study.

The present findings challenge results from some previous studies of change blindness in ASC that have reported no differences between groups or even greater change blindness in ASC [29–33] (Fletcher-Watson et al, 2006; Fletcher-Watson et al., 2008; Kikuchi et al., 2009; Loth et al., 2008; New et al., 2010). Mixed results across studies may be due to differences in methodologies and in characteristics of the samples [33,34] (Loth et al., 2008; Smith & Milne, 2008). For example, the task by Fletcher-Watson et al [29] (2006) utilized a ‘switch’ procedure which involved multiple response requirements throughout, which included pressing the space bar throughout each of the trials to progress from one image pair to the other, and then pressing further different buttons to stop the trial once the change was detected and to move to the next trial. Together, this may have increased task difficulty and EF demands compared to the traditional flicker paradigm and may have affected the results of that study, given the reported deficits of executive function in ASC [36,37] (Ozonoff, 1995; Ozonoff et al., 1991). A further change detection task [35] (Fletcher-Watson et al., 2012) and the present task both involved the same methodology where participants only had to press a button once during trials when they detected a change, which requires little cognitive demands during the task. Interestingly, both the present study and the one by Fletcher-Watson et al. [35] (2012) report about reduced change blindness in ASC to changes of marginal interest items, showing that methodology might be an important factor in studies of change detection in ASC.

The present study also found the greatest groups differences in detecting changes with location, where an item moved from one part of the scene to another across image alternations. This finding must be interpreted with caution for two main reasons. The first is that the groups also showed differences in the number of detected changes for the location types of changes, with the ASC group detecting approximately one fewer change compared to the controls. The second reason is that the images were not equated for detection difficulty across the different categories. However, it is still an interesting result for a couple of reasons. One reason is because changes of location often involve a wider area of the image compared to the other types of changes, as the change across images includes the original location of the scene where the image occurred along with the new location where the item appears in the changed image. In contrast, changes of colour and absence/presence involve changes occurring within the exact consistent location across images. So on the one hand, enhanced attention to detail may facilitate attention to changes of location in ASC because evidence of a change may appear across a wider area of the image compared to other types of changes, with some visual detail perhaps capturing the attention of those with ASC more readily than controls in most instances.

Another interesting reason is that many of the changes in location to marginal interest items occur in relation to items within the image that are of central interest (e.g. a bar that runs behind the two central people eating dinner in a scene and moves up and down across the two versions of the image). Therefore, detection of some changes in location within images may involve attention to relations between the marginal and central interest items, or shifting attention between the central and marginal items as the images change. Since those with ASC are reported to have difficulties in shifting attention [56,57] (Courchesne et al., 1994; Pascualvaca et al., 1998), widening their focus of attention [58] (Burack, 1994), or having an overly focused attention [15–17] (Robertson et al., 2013a,b,c), they may miss changes of location within certain scenes where relations to wider areas or aspects of the image in relation to the changing item are helpful to detect the change. This may help explain why the ASC group also had lower detection rates compared to the control group for changes to items of marginal interest that changed their location within the images, reflecting greater change blindness for detecting these types of marginal interest changes. This group difference reflected approximately 1 more change missed for the ASC group versus the controls for marginal interest changes of location, though there was no overall group difference in change detection in the study. This small but significant effect of greater change blindness in detection rates for location changes may be due to the ASC group having more difficulty on certain trials involving a change of location to marginal interest items where shifting attention or widening their focus of attention was a useful strategy. Further research to disentangle the factors determining when those with ASC show reduced change blindness versus greater change blindness is needed.

The longer latencies overall to detect marginal interest compared to central interest changes by both groups reveals a normal change blindness effect in ASC. This demonstrates that some degree of context or semantics about the information in the scenes was influencing attention processes in those with ASC. If context had no effect, we would have expected to see equivalent response times across both central and marginal changes in ASC, as their attention would be drawn to the physical characteristics of the changes and not influenced by the semantic aspects of the scene. The types of change and the low-level visual characteristics were well-matched between central and marginal interest conditions, therefore some degree of top-down influence was likely affecting attention in ASC. However, the present results show that attention in ASC is drawn more towards items of less interest in the scenes than the controls, suggesting that context had less effect in those with ASC than controls and that there may be differences in the nature of top-down influence for those with ASC. It should be noted that what counts as items of “more” or “less” interest itself depends on coding information for “relevance” [59] (Sperber, 1995), an ability linked to ‘theory of mind’ since a typical child or adult is constantly monitoring what is of social relevance to others. Thus, the current findings, whilst perceptual, may themselves be influenced by atypical social cognition in ASC [60] (Baron-Cohen et al., 2013).

A limitation of the present study is the use of longer latencies for displays compared to timings used in other studies of change blindness. We included the longer latencies because previous research has reported comparable change blindness effects are evident across both shorter and longer display times, including latencies similar to those used in the present study [3,4,41,43] (O’Regan et al., 1999; O’Regan et al., 2000; Rensink, 2000; Rensink et al., 2000), and because people with ASC often show slower responses compared to controls and have more difficulties with EF and decision-making. Although having longer latencies might help simplify the task and reduce the cognitive demands for those with ASC, it might also affect how they view the images and detect the changes in a way to favor those with ASC. However, another change detection study reported similar findings to the present study using shorter display timings of the images [35] (Fletcher-Watson et al., 2012). Further research is needed comparing different methodologies to test the effects of these factors on change detection in ASC.

Another limitation is that the present study included only male adults with ASC and participants generally had high IQ scores, so these results about reduced change blindness items of marginal interest may not generalize to other people with ASC. Therefore, further research is needed to test whether these results would be seen for other groups on the autism spectrum, including females and lower-functioning individuals. Future studies should incorporate other measures of gaze during the task, such as eye-tracking, to investigate overt attention by people with and without ASC. We conclude that we have found evidence for reduced change blindness in autism which represents superior change detection for items within scenes that are typically less salient.

Conclusions

The present study is the first experimental evidence we are aware of to demonstrate reduced change blindness in adults with ASC for changes occurring in scenes of everyday life. The enhanced detection of changes in ASC occurred for items within scenes that are normally of less interest for people to attend towards and subsequently remember. However, the ASC group also showed a small but significant reduction in detecting changes of location within the marginal interest condition compared to the controls. Together, these results are consistent with theories of enhanced perception of local details alongside reduced processing of the wider context in ASC, and with clinical and anecdotal reports that people with ASC show differences in attention towards small details in the environment that often appear insignificant to others.

Supporting information

Acknowledgments

We thank Bhismadev Chakrabarti, Teresa Tavassoli, Caroline Robertson, Jan Freyberg, Owen Parsons, and Marie Gomot for valuable discussions. The authors declare no competing financial interests.