Attention-related change in z-standardized accuracy and certainty.

<p>Differences of mean performance values across subjects observed for the valid condition minus those observed for the invalid condition plotted as Δ z-value (means ± standard errors of the mean). Positive <i>Δ</i>s reflect increases with attention. Both z-transformed accuracy and certainty increase significantly with attention for all four experiments. Certainty increases with valid cueing when correct and incorrect trials are analyzed separately. Increases of certainty are significantly larger than increases of accuracy (grey labels) for SN, SW and FN and tend to be in FW. Detailed p-values see main text. <i>(*)</i> tags p<0.1; <i>**</i> p<0.01; <i>***</i> p<0.001 derived from paired <i>t</i>-tests.</p

Determinants of the overall perceptual learning effect.

<p>Each subject’s overall learning effect as a function of the first (of nine) section’s (A) accuracy threshold, (B) certainty threshold, and (C) metacognitive sensitivity. The overall learning effect was parametrized as the difference between the perceptual accuracy threshold of section one and nine.</p

Z-standardized certainty increases significantly more with attention than z-standardized accuracy if controlled for the overall success rate.

<p><b>A</b>, Mean accuracy for the group of valid cue trials next to the mean accuracy for invalid cues, all subjects. B, Δ z-values for accuracy and certainty for overlapping coherences of the attended and the unattended condition when overall perceptual success rate is the same for the two cueing conditions. A, <b>B</b>, means ± standard errors of the mean.</p

Spatial attention: behavioral tasks and effects of attention on accuracy and certainty.

<p><b>A</b>, Timing of events for an example spatial attention trial. The test stimulus consisted of two RDKs presented simultaneously left and right of the fixation point (1.5 – 2s), level of motion coherence and direction of global motion (four alternatives) were modulated on a trial-by-trial basis. An arrow before stimulus presentation (0.5 – 1s) indicated which RDK covertly shift attention to, a second arrow after the stimulus (2.5 – 3s) instructed subjects which RDK they actually had to indicate the direction of coherent motion for. Valid cueing - as defined by congruent orientation of the attentional and the instructional cue - was applied in 80% of trials, see dark blue option. Invalid cueing (incongruent arrows, light blue option) was applied in the remaining 20% of trials. Subjects reported perceived motion direction with a first button press and decision certainty with either a second press of the same buttons using four predefined numerical ratings (SN) or of two of the buttons corresponding to a high (10) or low (1) wager (SW). For the separate wagering variation, wager feedback was given via a continuously updated point score adding or subtracting the chosen virtual bet. <b>B–I</b>, Percentage of correct responses or certainty index, respectively, vs. motion coherence for all subjects. Data points show the proportion of correct choices or the certainty index, respectively. Size of the points is scaled pursuant to the number of corresponding trials. Solid curves are logistic fits to the data using a Maximum Likelihood criterion. <i>**</i> tags p<0.01; <i>***</i> p<0.001 derived from model comparison statistics using Monte-Carlo simulations of the two respective fits, missing asterisk in h: no significant difference between fits. Spatial attention with numerical certainty ratings: B–E; spatial attention with certainty wager: F–I. B,F compare accuracy for valid and invalid cues. C,G compare certainty for valid and invalid cues. D,H compare accuracy and certainty for valid trials. E,I compare accuracy and certainty for invalid trials.</p

Metacognitive sensitivity, tACS sessions.

<p>Mean metacognitive sensitivity for the three experimental sessions: (A) chronological order, (B) by type of tACS stimulation. Metacognitive sensitivity was determined by a non-parametric signal detection theoretic approach, in which a higher area under the type 2 ROC curve (AUROC2) indicated higher metacognitive sensitivity. Data are mean of all subjects ± s.e.m.</p

Perceptual accuracy, choice certainty, and their correlation through the nine consecutive learning sections.

<p>(A) Each subject’s proportion of correct responses and (B) certainty index for the nine consecutive experimental sections. (C) Correlation of these accuracy and certainty thresholds through the time course of the experiment (nine sections), all subjects.</p

Perceptual accuracy and choice certainty, tACS sessions.

<p>(A) Proportion of correct responses and (B) certainty index for the three experimental sessions, chronological order. (C) Proportion of correct responses and (D) certainty index for the three experimental sessions by type of tACS stimulation. Data are mean of all subjects ± s.e.m.</p

Determinants of the incremental perceptual learning effect.

<p>Each subject’s incremental learning effect as a function of the preceding section’s (A) accuracy threshold, (B) certainty threshold, and (C) metacognitive sensitivity. The incremental learning effect was parametrized as the difference between the perceptual accuracy threshold of section n and section n+1 and related to the mean accuracy threshold, certainty threshold, or metacognitive sensitivity of section n.</p

Timeline of the behavioral task and transcranial alternating current stimulation (tACS).

<p>The test stimulus consisted of a random dot kinematogram presented at the center of the screen while eye movements were monitored (1000–1333 ms). The level of motion coherence and the direction of global motion (four alternatives) were modulated on a trial-by-trial basis. Subjects reported perceived motion direction with a first button press and decision certainty with a second button press corresponding to a high (10) or low (1) wager. Wager feedback was given via a continuously updated point score adding or subtracting the chosen virtual bet. As symbolized by the three different stimulation tracks below the stimulus schematic, tACS was delivered in three sessions using either 3 Hz stimulation with a phase angle of 0° or 180° relative to stimulus onset, or sham stimulation. The sequence of the sessions was permutated, the subjects were equally randomized to the resulting six groups.</p

Feature-based attention: behavioral tasks and effects of attention on accuracy and certainty.

<p><b>A</b>, Timing of events for an example feature-based attention trial. The test stimulus consisted of two interlacing RDKs differing in color and was presented randomly left or right of the fixation point (1–1.5 s), modulation of the independent RDKs otherwise matched the spatial attention tasks. Color changes of the fixation point to red or green before (0.5–1 s) and after the presentation (1.5–2 s) of this test stimulus instructed subjects which dot elements to direct attention to and which to actually indicate the direction of global motion for. The other cueing and response modalities were identical to the spatial attention tasks. <b>B–I</b>, Percentage of correct responses or certainty index, respectively, vs. motion coherence for all subjects. Conventions are identical to the spatial attention tasks in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041136#pone-0041136-g001" target="_blank">Fig. 1</a>. <i>*</i> tags p<0.05; <i>***</i> p<0.001 derived from model comparison statistics using Monte-Carlo simulations of the two respective fits, missing asterisk in I: no significant difference between fits. Feature-based attention with numerical certainty ratings (FN): B–E, feature-based attention with certainty wager (FW): F–I. B, F compare accuracy for valid and invalid cues. C, G compare certainty for valid and invalid cues. D, H compare accuracy and certainty for valid trials. E, I compare accuracy and certainty for invalid trials.</p