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Figures
- Fig. 1
Illustration of the flanker task and stimuli. Top: sequence of events within each flanker trial. The feedback always appeared exactly 1625 ms after the onset of the stimulus, with a fixed response window of 1000 ms. The 4 response keys are marked in yellow. Bottom: flanker stimuli containing information about the response hand (left or right, depending on the type of stimulus [triangle v. arrow]), the response finger (left or right, depending on the orientation of the central/target stimulus) and the action required (Go = button-press v. No-go = inhibition of motor response, depending on the colour). We switched assignment of stimulus type to response hand and colour to Go/No-go instruction between 2 blocks of the experiment for each participant (this example: Go = blue; left hand = triangle), and we counterbalanced the sequence of these assignments across participants.
- Fig. 2
Illustration of ERN/Ne (and CRN/Nc) findings. Left side: grand averages of response-locked potentials elicited by correct button-presses (thin blue lines) and errors (bold red lines) at electrode positions Fz, FCz, Cz and Pz for controls (upper 4 panels) and people with ADHD (bottom 4 panels); y-axis with unit μV. For illustration purposes, we applied a 30 Hz low-pass filter (x-axis 0 marks the correct/error button- press). Topographical maps show the field distribution of the ERN/Ne (blue field, left) and subsequent Pe (red field, right). The middle panel on the right illustrates a significant group × position interaction indicated by the ANOVA on ERN/Ne amplitudes. **Indicates a significant group difference for mean correct/error potentials at electrode position Fz, p < 0.01. ADHD = attention-deficit/hyperactivity disorder; ANOVA = analysis of variance; CRN/Nc = correct response negativity; Cz = central electrode position; ERN/Ne = error-related negativity/error negativity; FCz = frontocentral electrode position; Fz = frontal electrode position; Pe = error positivity; Pz = parietal electrode position.
- Fig. 3
Illustration of P300 findings. Top: grand averages of ERPs elicited by flanker stimuli following either correct responses (thin blue line) or errors (bold red line) on the previous trial (0 marks the stimulus presentation); note the pronounced P300 component that was significantly smaller after errors v. correct responses (main effect condition). Bottom: stimulus-elicited ERPs at electrode positions Cz (bold red lines) and Pz (thin blue lines) in controls (left) and people with ADHD (right), illustrating a group × position interaction. (Depicted here: trials following correct responses; similar effects were also observed on post-error trials.) Maps show the field distribution of the P300 at the peak of the GFP. ADHD = attention-deficit hyperactivity disorder; Cz = central electrode position; ERP = event-related potential; GFP = global field power; Pz = parietal electrode position.
- Fig. 4
Illustration of CNV effects in the ITI. Top: grand average of the ITI following either error (solid lines) or correct responses (dotted lines) in Go trials for people with ADHD (thin blue lines) and controls (bold red lines) at position Cz (0 marks the beginning of the next trial: Go or No-go flanker stimulus). Note the reduced CNV in people with ADHD (v. controls) that occurred specifically after errors (comparison of the 2 solid lines; p < 0.01). Bottom: grand averages locked to the feedback stimulus directly preceding the ITI, for feedback indicating correct responses (dotted lines) and errors (solid lines) in people with ADHD (thin blue lines) and controls (bold red lines). While the type of feedback affected the resulting ERP, groups showed no discernible differences; therefore, group differences in feedback processing were unlikely to explain subsequent group differences in CNV for ITIs after error trials. ADHD = attention-deficit/hyperactivity disorder; CNV = contingent negative variation; Cz = central electrode position; ERP = event-related potential; FB = feedback; ITI = intertrial interval.
Tables
Characteristic Control (n = 34) ADHD (n = 34) Test statistic with effect size (group comparison) Age, yr, mean ± SD 27.62 ± 7.43 30.29 ± 9.47 t66 = 1.30, NS; d = 0.31 IQ, mean ± SD* 118.6 ± 15.7 115.7 ± 14.6 t65 = −0.79, NS; d = −0.19 Years of education, mean ± SD† 12.88 ± 1.21 12.75 ± 0.76 t54 = −0.51, NS; d = −0.13 ASRS hyperactivity, mean ± SD‡ 8.7 ± 4.3 20.5 ± 4.9 t66 = 10.60, p < 0.001; d = 2.56 ASRS inattention, mean ± SD§ 10.4 ± 4.3 24.6 ± 4.6 t66 = 13.15, p < 0.001; d = 3.19 I7 impulsivity, mean ± SD¶ 4.9 ± 2.2 11.9 ± 2.9 t66 = 10.66, p < 0.001; d = 2.72 Sex, female/male, no. 18/16 13/21 χ2 = 1.48, NS; V = 0.15 Handedness, right/left, no. 30/4 28/6 χ2 = 0.47, NS; V = 0.08 Smoker/nonsmoker, no. 10/24 11/22** χ2 = 0.12, NS; V = 0.04 ADHD = attention-deficit/hyperactivity disorder; ASRS = Adult ADHD Self-Report Scale; I7 = Eysenck’s Impulsiveness Questionnaire; IQ = intelligence quotient; NS = not significant; SD = standard deviation.
↵* IQ was assessed based on the Mehrfachwahl-Wortschatz Intelligenztest (information missing for 1 participant).
↵† Information missing for 3 participants.
↵‡ Hyperactivity subscale of the Adult ADHD Self-Report Scale.
↵§ Inattention subscale of the Adult ADHD Self-Report Scale.
↵¶ Impulsivity subscale of Eysenck’s Impulsiveness Questionnaire I7 (data missing for 4 people with ADHD and 2 controls).
↵** Information missing for 1 participant.
Measure, mean ± SD Controls (n = 34) ADHD (n = 34) Test statistic with effect size (group comparison) Mean RT, ms 504.74 ± 90.13 532.32 ± 87.62 Z = 1.41, NS; d = 0.31 RT post-correct, ms 509.59 ± 97.17 532.85 ± 91.92 t66 = 1.01, NS; d = 0.25 RT post-error, ms 531.18 ± 90.61 576.79 ± 111.06 t66 = 1.86, p < 0.1; d = 0.45 SD-RT, ms 110.97 ± 26.26 127.44 ± 29.50 Z = 2.49, p < 0.05; d = 0.59 SD-RT post-correct, ms 107.71 ± 23.94 124.88 ± 29.83 Z = 2.58; p < 0.01; d = 0.63 SD-RT post-error, ms 119.09 ± 50.29 130.38 ± 44.84 Z = 0.80, NS; d = 0.24 Total errors, no. 40.56 ± 23.36 53.00 ± 28.67 Z = 1.77, p < 0.1; d = 0.48 Errors post-correct, no. 24.06 ± 15.45 31.12 ± 16.58 Z = 1.85, p < 0.1; d = 0.44 Errors post-error, no. 5.29 ± 5.20 8.97 ± 9.01 Z = 1.60, NS; d = 0.50 PES(traditional), ms 21.59 ± 58.53 43.94 ± 61.64 t66 = 1.53, NS; d = 0.37 PES(robust), ms 28.97 ± 29.91 44.74 ± 43.64 t66 = 1.74, p < 0.1; d = 0.42 ADHD = attention-deficit/hyperactivity disorder; NS = not significant; PES(robust) = more robust measure of post-error slowing (mean RTs on individually paired post-error trials [E + 1] – pre-error trials [E − 1]; see methods section); PES(traditional) = traditional measure of post-error slowing (mean RTs after incorrect responses – mean RTs after correct responses); RT = reaction time to Go stimuli (only correct responses included); SD = standard deviation; SD-RT = standard deviation of reaction times to Go stimuli (only correct responses included).
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