109 Local-global visual processing in ASD

characteristic of ASD (Constantino & Gruber, 2005; Roeyers et al., 2011). 0[ JVUZPZ[Z VM Ä]L ZVJHSSLK º[YLH[TLU[ ZJHSLZ»! :VJPHS (^HYLULZZ :VJPHS Cognition, Social Communication, Social Motivation and Autistic Mannerisms. By applying factor analysis Frazier et al. (2012) demonstrated that a 2-factor model, dividing SRS social and autistic mannerisms scales consistent with DSM-5 ‘social communication/interaction’ and RRBIs domains, best explains the variance in SRS scores. Accordingly, we summed the scores of the ‘social’ scales to obtain one index of social (communication and interaction) ASD symptoms, while the score on the Autistic Mannerisms scale was taken as an index of RRBIs.

The 9LWL[P[P]L)LOH]PVY:JHSL¶9L]PZLK9):9 assesses the RRBIs VIZLY]LK PU PUKP]PK\HSZ ^P[O (:+ )VKÄZO L[ HS  ( KPZ[PUJ[PVU PZ THKLIL[^LLUKPɈLYLU[Z\IZJHSLZ:[LYLV[`WLK:LSMPUQ\Y`*VTW\SZP]L Ritualistic, Sameness and Restricted Behaviour), but we only report the total score. The questionnaire was translated to Dutch by translation and back-translation.

2.3. Procedure

Participants were tested individually in a quiet room, either at the University Hospital or at school. Besides the tasks described above, additional executive functioning tasks were administered for another study (Van Eylen, Boets, Steyeart, Wagemans, & Noens, submitted). The whole testing took about four hours, divided into four 1-h sessions. Enough breaks were provided to avoid fatigue. Additionally, computerized tasks were alternated with other [HZRMVYTH[Z[VWYV]PKLLUV\NO]HYPH[PVU;VH]VPKVYKLYLɈLJ[Z[OLVYKLY of sessions and the order of tasks within a session were counterbalanced. Participants received a small reward for their participation.

Computerized tasks were run on a Dell Latitude E6400 notebook. For the FOO task, children were seated 50 cm from the notebook’s screen, set to pixel resolution 1024 by 768 at 75 Hz refresh rate. For the other computerized tasks, a 17-inch Elo Entuitive touch screen was used at a pixel resolution of 1280 by 1024 (640 by 480 for the CM task) and a 60 Hz refresh rate. The distance from the touch screen was 57 cm, except for the VS task for which a distance of 40 cm was used to ensure that even the smallest children JV\SK[V\JO[OLZJYLLU;OL]PL^PUNHUNSLVM[OLJVTW\[LYZJYLLU^HZ ‡ ensuring good stimulus visibility.

Questionnaires were completed by the participants’ parents.

2.4. Data analyses

Prior to analysis, appropriate transformations (square root or logarithm base 10) were applied if necessary to obtain normally distributed variables. In the tables, the values for the mean and standard deviations result from the raw, non-transformed variables. For the RT data, only the correct trials were used and within-subject outliers (>2.5 SD of the participant’s own mean) were excluded. Group outliers (>2.5 SD of the group mean) were excluded for all variables. Analyses were performed with and without exclusion of outliers.

110 Local-global visual processing in ASD

If analyses with and without outlier exclusion yielded the same results, only analyses including group outliers are reported. Otherwise, results of both analyses are mentioned.

For normally distributed local-global and control measures, we PU]LZ[PNH[LK[OLLɈLJ[VMNYV\W(:+]Z;+HNLJOPSKYLU]ZHKVSLZJLU[Z gender and all two-way interactions. The three-way interaction between group, age and gender was not included in the model, because the number of observation in each cell was too small to produce reliable results. An adapted backward model selection procedure was applied. Starting from the full TVKLSPUJS\KPUNHSSLɈLJ[Z[OLLɈLJ[Z^P[OHW]HS\L™^LYLZ\IZLX\LU[S` LSPTPUH[LK-VY[OLYLTHPUPUNLɈLJ[ZHSSWVZZPISLTVKLSJVTIPUH[PVUZ^LYL Ä[[LKHUK[OLILZ[TVKLS^HZZLSLJ[LKIHZLKVU[OL(RHPRLHUK)H`LZPHU Information Criteria (AIC and BIC respectively; Burnham & Anderson, 2004). 6US`[OPZÄUHSILZ[TVKLSPZYLWVY[LK:PUJL[OLLɈLJ[VMNYV\W^HZV\YTHPU interest, it was always included in the model.

-VY [OL =: HUK [OL -66 [HZRZ ^L HKKP[PVUHSS` L_HTPULK [OL LɈLJ[ of several within-subject factors. To reduce the number of factors in the full TVKLS^LÄYZ[KL[LYTPULK[OLÄUHSILZ[TVKLSJVU[HPUPUNVUS`[OLIL[^LLU subject factors, following the backward model selection procedure described HIV]L(M[LY^HYKZ[OPZÄUHSTVKLS^HZJVTWSLTLU[LK^P[OHSS^P[OPUZ\IQLJ[ factors and the interactions between these and the between-subject factors MYVT [OL ÄUHS TVKLS 6U [OPZ ºUL^ M\SS TVKLS» ^L [OLU HNHPU HWWSPLK [OL IHJR^HYKTVKLSZLSLJ[PVUWYVJLK\YLWYL]PV\ZS`KLZJYPILK[VVI[HPUHÄUHS model containing both within- and between-subject factors. To reduce this ‘new full model’ for variables of the FOO task, we did not examine interactions between the four within-subject variables.

ANOVA was applied to analyse performance on the CM and ROCF task. Repeated-measures mixed model analyses (with Kenward-Roger method to JHSJ\SH[LKLNYLLZVMMYLLKVT^LYL\ZLK[VHUHS`ZL[OL[HYNL[PKLU[PÄJH[PVU SH[LUJ`MVY[OL=:[HZR[OLJVYYLJ[PKLU[PÄJH[PVUMYHTLHUKSH[LUJ`MVY[OL FOO task, and the RT on the control tasks. For scores that could not be transformed to a normal distribution (i.e., RBS-R scores and the proportion of unrecognized objects of the FOO task), non-parametrically Mann-Whitney <[LZ[Z^LYL\ZLK[V[LZ[[OLLɈLJ[VMNYV\W(:+]Z;+7VZ[OVJ[LZ[Z were corrected for multiple comparisons using Tukey-Kramer correction. A ZPNUPÄJHUJLSL]LSVMW#[^VZPKLK^HZHKVW[LKMVYHSSHUHS`ZLZ-VYHSS THPU SVJHSNSVIHS TLHZ\YLZ *VOLU»Z K NYV\W LɈLJ[ ZPaLZ ^LYL JHSJ\SH[LK I`KP]PKPUN[OLLZ[PTH[LKNYV\WKPɈLYLUJL3LHZ[:X\HYL4LHUZPU[OLÄUHS TVKLSI`[OLWVVSLKZ[HUKHYKKL]PH[PVU©Bˈ₁õˈ₂õD(ULɈLJ[ZPaLYHUNPUN from 0.2 to 0.3 is considered small, values around 0.5 are medium and values VMVYHIV]LHYLJVUZPKLYLKSHYNLLɈLJ[Z*VOLU 

To investigate the association between the local-global measures, we calculated zero-order and partial Pearson correlations, the latter controlling MVY[OLLɈLJ[VMHNLHUK-:08(KKP[PVUHSS`^LHWWSPLKYLNYLZZPVUHUHS`ZLZ [V [LZ[ ^OL[OLY [OLZL JVYYLSH[PVUZ IL[^LLU SVJHSNSVIHS TLHZ\YLZ KPɈLYLK for both groups. To examine the association between local-global measures

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