No evidence of reaction time slowing in autism spectrum disorder

Abstract

A total of 32 studies comprising 238 simple reaction time and choice reaction time conditions were examined in individuals with autism spectrum disorder (n = 964) and controls (n = 1032). A Brinley plot/multiple regression analysis was performed on mean reaction times, regressing autism spectrum disorder performance onto the control performance as a way to examine any generalized simple reaction time/choice reaction time slowing exhibited by the autism spectrum disorder group. The resulting regression equation was Y (autism spectrum disorder) = 0.99 × (control) + 87.93, which accounted for 92.3% of the variance. These results suggest that there are little if any simple reaction time/choice reaction time slowing in this sample of individual with autism spectrum disorder, in comparison with controls. While many cognitive and information processing domains are compromised in autism spectrum disorder, it appears that simple reaction time/choice reaction time remain relatively unaffected in autism spectrum disorder.

Keywords

autism spectrum disorder simple reaction time/choice reaction time slowing

The literature on autism spectrum disorder (ASD) suggests a wide variety of cognitive, social and behavioral deficiencies (Schmitz et al., 2007). Central to many of these deficiencies is that reaction time (RT) would also be compromised, as RT (simple reaction time (SRT) as well as choice reaction time (CRT)) and speed of processing are critical underlying mechanism tying various cognitive abilities and functions together. SRT involves the participant making a single response to a stimulus, and the instructions in such a task would state that when the participant sees or hears the stimulus, they need only press the spacebar on the computer. CRT, on the other hand, involves the participant making a decision with regard to which key on a keyboard to press. A typical CRT task may instruct the participant to press the “z” key when a red stimulus appears on the computer screen and to press the “m” key when a green stimulus appears on the computer screen. Thus, they have to make a decision (or choice) on which key to press. No such decision is involved in the SRT task. While RT is a fundamental component of information processing, results with individuals with ASD are often at odds with regard to what aspects of RT slow and what aspects do not slow.

For instance, individuals with ASD are faster at processing visual-spatial information than controls (Kaland et al., 2007). Likewise, the attentional system of individuals with ASD operates differently such that individuals with ASD are also faster at certain visual search tasks (Landry et al., 2009) than controls. At higher conceptual levels of information processing (i.e. word meaning), however, individuals with ASD are typically much slower than controls (Spiers et al., 2011). Since RT forms the basis of many cognitive tasks, abilities, and processes, and given that individuals with ASD do not always show evidence of information processing impairments on some processes that involve RT, further investigation of the role RT plays in individuals with ASD seems important.

One methodology to examine RT similarities and differences within and between groups is the so-called Brinley (1965) plot analysis. Such Brinley plots often compare younger and older adults, for instance, across several experimental conditions in which both groups of subjects participated in Myerson et al. (1994). Additionally, several conditions from many experiments are combined into a single Brinley plot to show the extent of RT slowing. Much like multiple regression, Brinley plots result in a mathematical function represented by the equation Y = mX + b (where Y represents the RT latencies for younger adults, X represents the RT latencies from older adults, m represents the coefficient of slowing, also referred to as the slope value, and b indicates where this best fit regression line crosses the Y axis). Like regression, an R² value is also calculated and represents the amount of variance accounted for by the specific bet-fit regression line through the various group data points. Thus, the slope value can be used as an index of slowing and has been used widely in studies of aging and closed-head injury to name but a few. A slope of 1.0 would indicate, for instance, no slowing between two groups of subjects, while a slope of 1.5 would indicate that one group was 1.5 times slower than another group. Likewise, a slope of 1.6 would indicate that one group was 1.6 times slower than another group. For instance, Ferraro (1996) examined mean RTs from 13 studies which included n = 353 closed-head-injury subjects and n = 329 control subjects and found that Y (CHI) = 1.54X (control) − 59, which suggests that for this specific sample, the CHI subjects were approximately 1.54 times slower than the control subjects across RT conditions in which both groups participated. This function accounted for 89% of the variance. Thus, the Brinley plot methodology can be applied to groups of subjects to further investigate the extent (or lack thereof) of what has been termed general slowing.

In this study, we applied the Brinley plot methodology to the ASD literature to test the hypothesis that there is a general slowing accompanying ASD in cognitive tasks that require RT as a dependent variable. No such Brinley plot analysis has been performed in the ASD literature, and its use in this literature may shed light on more recent developments suggesting that some cognitive processes are spared in ASD, while others are not.

Methods

A total of 32 studies (see Table 1) comprising 238 SRT and CRT conditions were examined in individuals with ASD (n = 964) and controls (n = 1032). Google Scholar was employed as the search engine and was searched for the time frame 1997–2014 using the following search terms: Autism, ASD, RT, and reaction time. The following criteria were used to select studies: (1) studies chosen used either SRT or CRT as the dependent variable, (2) RTs could not be faster than 250 ms or slower than 5000 ms, (3) a comparable control group (non-ASD) was included that participated in the same set of experimental conditions, (4) at least 1 experimental condition common to both subject groups, and (5) RT values appeared in table form in the manuscript. Table 1 lists each study, the type of task (SRT, CRT), number of experimental conditions in which the ASD and control groups each participated, sample characteristics, and how the diagnosis of ASD was made based on the search criteria listed above.

Table 1.

Characteristics of studies used in the present Brinley plot analysis.

Study 1: Adams and Jarrold (2012)

Tasks: Choice reaction time (CRT), prepotent response signal stop-signal, modified flanker

Conditions: 19

ASD: N = 15 (12 males), M age = 9 years and 10 months; matched for non-verbal mental ability; M Raven’s (Raven, 1969; Raven et al., 1990) colored progressive matrices (RCPM) = 25.86

Control: N = 15 typically developing (4 males), M age = 14 years and 5 months; matched for non-verbal mental ability; M RCPM = 24.53

Study 2—Ashwin et al. (2005)

Tasks: CRT, facial emotion and identity chimeric faces

Conditions: 4

ASD: Experiment 1 (N = 16 males, M age = 26.8 years, Full Scale IQ (FSIQ) = 118.4); Experiment 2 (N = 15 males, M age = 26.7 years, FSIQ = 117.4); formal diagnosis of autism according to international criteria (APA, 1994, 2000)

Control: Experiment 1 (16 males, M age = 28.3 years, FSIQ = 117.7); Experiment 2 (15 males, M age = 28.3 years, FSIQ = 118.0)

Study 3—Bar-Haim et al. (2006)

Task: simple reaction time (SRT) probe detection

Conditions: 8

ASD: N = 12 (all male), M age = 10.17 years, FSIQ = 96.1; met diagnostic criteria of the Autism Diagnostic Interview (ADI) (Lord et al., 1994)

Control: N = 12 (all male); M age = 10.19 years, FSIQ = 102.5

Study 4—Bogte et al. (2009)

Task: CRT, recognition memory

Conditions: 4

ASD: N = 36 (29 males), M age = 26.66 years, FSIQ = 103.08; (Lord, 1997; Lord et al., 2000) criteria used for diagnosis

Control: N = 32 (14 males), M age = 28 years, FSIQ = 101

Study 5—Brian et al. (2003)

Task: CRT, negative priming

Conditions: 6

ASD: N = 23 (20 males), M age = 21.7 years, M RSPM = 39.2, M Peabody Picture Vocabulary Test-revised (PPVT-R) = 39.2 (Dunn and Dunn, 1981), diagnosed by an experienced child psychiatrist or developmental pediatrician with expertise in ASD

Control: N = 23 (20 males); M age = 19.2 years, M RSPM = 48.4, M PPVT-R = 110.9

Study 6—Chien et al. (2014)

Task: SRT, Conners’ Continuous Performance Test—impulsivity reaction time

Conditions: 1

ASD: N = 216 (191 males), M age = 10.4 years, M FSIQ = 89.49, clinically diagnosed with ASD using DSM-IV criteria

Control: N = 226 (180 males), M age = 11.8 years, M FSIQ = 111.95

Study 7—Cook and Bird (2012)

Task: CRT, automatic imitation

Conditions: 8

ASD: N = 19, M age = 40.9 years, M FSIQ = 112.94, written diagnosis from an independent clinician

Control: N = 22, M age = 34.91 years, M FSIQ = 118.26

Study 8—Falter et al. (2008)

Tasks: CRT, mental rotation, targeting, figure-disembedding

Conditions: 3

ASD: N = 28 (27 males), M age = 12 years and 5 months, M RCPM = 43.33, diagnosed by trained clinicians using DSM-IV-TR criteria

Control: 31 (30 males), M age = 12 years and 6 months, M RCPM = 44.33

Study 9—Geurts et al. (2008)

Task: CRT, change task

Conditions: 1

ASD: N = 25 (23 males), M age = 9.3 years, M FSIQ = 106.8, diagnosis confirmed by DSM-IV and Autism Diagnostic Interview-Revised (ADI-R)

Control: N = 85 (65 males), M age = 9.1 years, M FSIQ = 111.6

Study 10—Glasebrook et al. (2009)

Task: SRT, eye–hand coordination

Conditions: 3

ASD: N = 13 (11 males), M age = 23.4 years; M RCPM = 79.4, diagnosed by a qualified health professional using the DSM-III or DSM-IV criteria

Control: N = 15 (13 males), M age = 23.4 years

Study 11—Henderson et al. (2011)

Task: SRT, cross-modal semantic priming

Conditions: 16

ASD: N = 17 (15 males), M age = 11.62 years, M RCPM = 51.65, diagnosis confirmed using DSM-IV criteria

Control: N = 17 (14 males), M age = 11.50, M RCPM = 48.71

Study 12—Koldewyn et al. (2013)

Task: CRT, hierarchical local/global processing

Conditions: 12

ASD: N = 45 (36 males), M age = 8.83 years, M Performance IQ (PIQ) = 109.42, diagnosed by clinicians specializing in neurodevelopmental disorders

Control: N = 45 (36 males), M age = 8.19 years, M PIQ = 111.69

Study 13—Landry et al. (2009)

Task: CRT, visual orienting paradigm

Conditions: 8

ASD: N = 18, M age = 11.52, M PIQ = 99.50, M Performance Mental Age (PMA) 11.51, diagnosed using DSM-IV criteria

Control: N = 16, M age = 11.00 years, M Performance IQ (M PIQ) = 114.44, M PMA = 12.49

Study 14—Loucas et al. (2010)

Task: CRT, speech perception, non-word discrimination

Conditions: 4

ASD: N = 17 (10 males), M age = 176.3 months, diagnosis made on the basis of ICD-10 (World Health Organization (WHO), 1993) criteria using the ASD-R (Lord et al., 1994) and ADOS (Lord et al., 2000)

Control: N = N = 16 (16 males); M age = 172.7 months

Study 15—Mottron et al. (2003)

Task: SRT, global/local visual tasks

Conditions: 12

ASD: N = 12 (11 males); M age = 15.17 years, M FSIQ = 109.58, diagnosis based on ADI or ADI-R (Lord et al., 1989)

Control: N = 12 (12 males), M age = 15.33 years, M FSIQ = 105.42

Study 16—Mottron et al. (1999)

Task: CRT, whole versus part object processing

Conditions: 10

ASD: N = 11 (10 males), M age = 14.93 years, M RCPM = 110.91, M Global IQ = 100.64, diagnosed using the ADI or ADI-R (Lord)

Control: N = 11 (10 males), M age = 10.7 years, M RCPM = 116.09

Study 17—Norbury (2005)

Task: CRT, dominant/subordinate word meanings, suppression of irrelevant word meanings

Conditions: 8

ASD: N = 20; M age = 13.07 years, M Wechsler Abbreviated Scales of Intelligence (M WASI) = 106.80, used Social Communications Questionnaire (Berument et al., 1999)

Control: N = 28, M age = 12.46, M WASI = 107.41 (Wechsler, 1999)

Study 18—Nyden et al. (1999)

Task: CRT, go/no go visual/verbal

Conditions: 4

ASD: N = 10 (10 males); M age = 10.1 years, M PIQ = 91.6, M FSIQ = 100.7, diagnosed at consensus case conferences after comprehension examination by child psychologist, child psychiatrist, speech pathologist, and special education teacher

Control: N = 10 (10 males), M age = 10.0 years

Study 19—Olu-Lafe et al. (2014)

Task: CRT, silhouette-to-shape matching task, higher-order shape integration task

Conditions: 2

ASD: N = 20 (20 males), M age = 20.1 years, M Full IQ Kaufman Brief Intelligence Test (KBIT) = 105.3 (Kaufman and Kaufman, 2004), M Verbal IQ = 100/5, M Non-Verbal IQ = 108.4, diagnosed by a clinician and met DSM-IV-TR criteria, diagnosis confirmed by ADOS

Control: N = 20 (20 males), M age = 19.6 years, M Full IQ KBIT = 101.6, M Verbal IQ = 100.1 M Non-Verbal IQ = 102.2

Study 20—Ozonoff and Strayer (1997)

Task: CRT, stop-signal, negative priming

Conditions: 6

ASD: N = 13, M age = 13.9 years, M Verbal IQ (MVIQ) = 98.6, M PIQ = 103.7, M FSIQ = 101.0, met DSM-IV criteria for AD

Control: N = 13, M age = 13.1 years, M VIQ = 101.6, M PIQ = 98.2, M FSIQ = 100.1

Study 21—Pascualvaca et al. (1998)

Task: CRT, continuous performance, same-different computerized task, and computerized matching task

Conditions: 6

ASD: N = 23 (15 males), M age = 8.7 years, M VIQ = 74.4, M PIQ = 84.7, M FSIQ = 77.6, met DSM-II-R criteria for autistic disorder, scored above criteria for Childhood Autism Rating Scale (Schopler et al., 1988)

Control: N = 23, M age = 5.11 years, M VIQ = 106/1, M PIQ = 107.5, M FSIQ = 107.6

Study 22—Piggot et al. (2004)

Task: CRT, emotion match task

Conditions: 2

ASD: N = 14 (14 males), M age = 13.1 years, M FSIQ = 112, M VIQ = 104, M PIQ = 118, met DSM-IV criteria for ASD, met ADI-R criteria

Control: N = 10 (10 males), M age = 14.4 years, M FSIQ = 116, M VIQ = 114, M PIQ = 114

Study 23—Puts et al. (2014)

Task: SRT, CRT, tactile processing

Conditions: 2

ASD: N = 67 (54 males), M age = 10.08 years, FSIQ = 103.13, met DSM-IV criteria for ASD, confirmed with ADOS-G and ADI-R

Control: N = 32 (27 males), M age = 10.7 years, FSIQ = 117.33

Study 24—Remington et al. (2012)

Task: CRT, selective attention

Conditions: 16

ASD: N = 30 (21 males), M age = 24.3 years; WASI FSIQ = 115, met DSM-IV criteria for ASD, confirmed with Module 4 from ADOS

Control: N = 30 (21 males); M age = 26.45 years, WASI FSIQ = 118

Study 25—Schilbach et al. (2012)

Task: SRT, spatially congruent/incongruent motor task to faces

Conditions: 6

ASD: N = 29 (17 males), M age = 32.0 years, M IQ = 110.70, diagnosed using ICD-10 criteria

Control: N = 28 (12 males), M age = 29.96 years, M IQ = 113.93

Study 26—Schmitz et al. (2007)

Task: CRT

Conditions: 3

ASD: N = 9 (9 males), M age = 38 years, M FSIQ = 105, M VIQ = 99, M PIQ = 108, diagnosed with ADI

Control: N = 12 (12 males), M age = 39 years, M FSIQ = 106,, M VIQ = 104, M PIQ = 108

Study 27—Solomon et al. (2008)

Task: CRT

Conditions: 16

ASD: N = 31 (28 males), M age = 12.3 years, M VIQ = 110, M PIQ = 108, M FSIQ = 110, diagnosed using ADOS-G

Control: N = 32 (29 males), M age = 12.2 years, M VIQ = 116, M PIQ = 112, M FSIQ = 115

Study 28—Spiers et al. (2011)

Task: SRT

Conditions: 4

ASD: N = 11 (11 males), M age = 14 years and 11 months, M FSIQ = 106.6, M VIQ = 108.1, M PIQ = 109.6, diagnosed with DSM-IV-TR

Control: N = 11 (11 males), M age = 14 years and 8 months, M FSIQ = 105.0, M VIQ = 104.6, M PIQ = 104.2

Study 29—Stauder et al. (2011)

Task: CRT

Conditions: 9

ASD: N = 22 (19 males), M age = 9.82 years, diagnosed using DSM-IV

Control: N = 22 (19 males), M age = 10.5 years

Study 30—Stoit et al. (2011)

Task: SRT

Conditions: 3

ASD: N = 28, M age = 11.6, M FSIQ = 100.3, diagnosed using DSM-IV, ADI-R, and ADOS-G

Control: N = 28, M age = 11.6, M FSIQ = 111.9

Study 31—Wallace et al. (2006)

Task: CRT

Conditions: 15

ASD: N = 24 (21 males), M age = 32 years, M RCPM IQ = 102, diagnosed using ICD-10 and ADI-R criteria

Control: N = 26 (23 males), M age = 31 years, M RCPM IQ = 98

Study 32—Williams et al. (2013)

Task: SRT

Conditions: 12

ASD: N = 75, diagnosed using ADI or ADI-R, ADOS

Control: N = 75

DSM-III: Diagnostic and Statistical Manual of Mental Disorders (3rd ed.); DSM-II-R: Diagnostic and Statistical Manual of Mental Disorders (2nd ed. rev.); DSM-IV: Diagnostic and Statistical Manual of Mental Disorders (4th ed.); DSM-IV-TR: Diagnostic and Statistical Manual of Mental Disorders (4th ed., text rev); ICD-10: International Classification of Diseases, Tenth Revision; ADOS: Autism Diagnostic Observation Schedule; ADOS-G: Autism Diagnostic Observation Schedule-Generic; AD: Alzheimer’s Disease; M RSPM: Raven’s Standard Progressive Matrices.

Results and discussion

Across the 32 studies, the mean SRT/CRT for each of the 238 experimental conditions was tabulated between ASD and non-ASD groups. These points were then plotted as (X, Y) coordinates and the best-fitting regression equation (ASD data regressed onto the corresponding non-ASD/control data) was fitted to these 238 points (see Brinley plot in Figure 1). The best-fitting equation that resulted was the following: Y (ASD) = 0.99X (non-ASD) + 87.93, R² = 92.3%. Our results show that, in the sample of studies included in this analysis, there is little if any SRT/CRT slowing associated with individuals with ASD.

Figure 1.

Mean SRT/CRT response times (in milliseconds) of individuals with ASD as a function of control individuals across 238 conditions.

This is the first study to use Brinley plot methodology to examine RT (SRT and CRT) slowing issues in ASD individuals. It supports the notion that not all cognitive abilities decline in ASD, especially as they relate to RT. The Brinley plot methodology has been used in developmental and aging studies for many decades, as well as in the examination of studies examining slowing in age-related diseases such as Alzheimer’s diseases (ADs). Such studies have been influential in the literature and have shown that slowing ratios often differ depending on which specific cognitive abilities are being examined and come to the conclusion that slowing is not a general consequence of aging and/or disease. Some processes slow with age and disease, while others do not. In other words, slowing is not general, but rather specific to the task at hand.

While this study only examined RT (SRT and CRT) slowing in individuals with ASD and did not examine specific tasks above and beyond whether they included SRT and CRT conditions, these results suggest little if any slowing in individuals with ASD. This is an important and relevant contribution to the ongoing discussion and debate regarding aspects of cognitive function that are impacted by ASD. ASD results in deficits in social communication, social interaction (American Psychiatric Association (APA), 2013) and many non-social perceptual and cognitive abnormalities. That RT is relatively preserved (based on the present Brinley plot analysis with the resulting slope of 0.99) is suggestive that the cognitive declines often observed in individual with ASD are not general and all-encompassing. That is, the RT components of the underlying cognitive processes appear preserved, based on the present analysis, and it is likely that processes beyond RT are those that are potentially compromised in individuals with ASD.

Future studies employing Brinley plot analysis could examine the slowing ratios of individuals with ASD across a wider range of tasks covering the entire information processing sequence, and not just RT. It may be that the slowing ratio in individuals with ASD varies as a function of type of information processing system or sequence being engaged by a specific task. Likewise, only 32 studies were used in this study, although typical criteria from other similar studies were employed. A more fine-grained article selection process could also have been used.

Despite these limitations, this study is the first to explore RT slowing in individuals with ASD. It was observed that there appears to be very little RT slowing in this group, based on Brinley plot methodology and analysis (e.g. slope value equals 0.99). These results can stand as a starting point to further investigate the impact ASD has on slowing (or lack thereof) across various cognition domains, thereby adding to the accumulating evidence of cognitive processing in individuals with ASD. These results also add to the discussion of assessment issues with individuals with ASD such that inclusion of RT tasks (SRT, CRT) in batteries of cognitive tasks would be helpful with regard to clinical assessment and clinical precision in psychological and neuropsychological investigations (see Mahurin and Pirozzolo, 1986). Such SRT and CRT measures would add valuable information with regard to clinical assessment and diagnostic issues.

Footnotes

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

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