Temporal Stability and the Effects of Training on Saccade Latency in “Express Saccade Makers”

The temporal stability of saccade latency, and the effects of training, particularly in “express saccade makers” (ESMs), has received little attention. ESMs are healthy, naïve, adults, who persist in executing very many low latency “express saccades” (ES; saccades with latency of 80 ms to 130 ms), in conditions designed to suppress such responses. We investigated the stability of ES production (%ES) in 59 ESM and 54 non-ESM participants in overlap tasks. Within a single session, the intraclass correlation coefficient (ICC) for %ES in two runs of 200 trials was 0.97 (p30% of saccades over the two runs were ES, were classified as ESMs. For 60 participants tested over two sessions 12 weeks apart, and 30 participants tested in three sessions over approximately six months, the ICC for %ES was uniformly high (0.95, p<0.001 and 0.97, p<0.001 respectively) and participants behaved consistently with their initial classification. Fourteen participants (7 ESMs) were then exposed to training consisting of either gap or overlap tasks. Training increased %ES in both groups. However, when tested in overlap tasks, it was not sufficient to transform Normal participants into ESMs. We conclude that the pattern of saccade behaviour exhibited by ESMs constitutes a stable and distinct oculomotor phenotype

Cultural Diversity and Saccade Similarities: Culture Does Not Explain Saccade Latency Differences between Chinese and Caucasian Participants

A central claim of cultural neuroscience is that the culture to which an individual belongs plays a key role in shaping basic cognitive processes and behaviours, including eye movement behaviour. We previously reported a robust difference in saccade behaviour between Chinese and Caucasian participants; Chinese participants are much more likely to execute low latency express saccades, in circumstances in which these are normally discouraged. To assess the extent to which this is the product of culture we compared a group of 70 Chinese overseas students (whose primary cultural exposure was that of mainland China), a group of 45 participants whose parents were Chinese but who themselves were brought up in the UK (whose primary cultural exposure was western European) and a group of 70 Caucasian participants. Results from the Schwartz Value Survey confirmed that the UK-Chinese group were culturally similar to the Caucasian group. However, their patterns of saccade latency were identical to the mainland Chinese group, and different to the Caucasian group. We conclude that at least for the relatively simple reflexive saccade behaviour we have investigated, culture cannot explain the observed differences in behaviour

Distribution of saccade latency for the prosaccade overlap task in “express saccade makers” (ESMs) and non-express saccade maker (“NORM”) participants.

<p>A,B. Examples of individual distributions with summary parameters (mean±SD; median(IQR)), where N is the total number of observations. C,D. Average distributions for the two participant groups. The values plotted in each 10ms bin are the group mean±95% CI. The solid black line plots the mean, with grey lines showing ±95% CI. The vertical grey region indicates the express saccade latency range (80ms to 130ms). The intersubject mean of individual median saccade latency (±SD) and the intersubject %ES is shown for the two participant groups. N is the number of participants in the group. Note the different y-axis scales between A,B and C,D.</p

Effect of gap (A-E) and overlap (F-J) training (see Fig. 1 for details of the training regimes).

<p>Percentage of express saccades (%ES) is plotted against median saccade latency for ESM (</p><p></p><p></p><p><mn>●</mn></p><p></p><p></p>) and Norm (•) individual participants. For details of the relative timing of different tests in the two training regimes refer to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0120437#pone.0120437.g001" target="_blank">Fig. 1</a>. In plots showing overlap performance during gap (D,E) and overlap training (F-H), the horizontal dashed line is plotted at 30%.<p></p

Stability of %ES over three testing sessions.

<p>A. Grey lines: individual participant data (broken lines: ESMs; solid lines: Norms). Black lines and points: group data, shown as the mean±95% CI (ESM ■; Norm ●). Black dashed line shows the 30% criterion level. B. 3D correlation plot of %ES over three sessions for ESMs (</p><p></p><p></p><p><mn>●</mn></p><p></p><p></p>) and Norms (●).<p></p

Plots of Schwartz Value Survey (SVS) results.

<p>Mean±95% CI value scores for each of the ten “values” for each participant group are plotted (CC: participants born and educated in China; N = 38; BC: Chinese ethnic background, born in the UK [or moved in early life], educated in the UK, N = 43; WB: Caucasian comparison group, N = 42). Group scores were compared with a one-way ANOVA for each value. Statistically significant results were observed for all values except “Security”. Marked values (*) are those for which post-hoc testing demonstrated that the BC and WB groups were similar and statistically distinct from the CC group. This was true for 5/9 values returning statistically significant ANOVA results.</p

Effect of gap (A-D) and overlap (E-F) training on group data.

<p>Intersubject mean±95%CI saccade median latency (A,B,E,F) and intersubject mean±95% CI %ES (C,D,G,H) for ESM (</p><p></p><p></p><p><mn>●</mn></p><p></p><p></p>) and Norm (●) groups is shown. To improve clarity, error bars are only plotted in one direction where they would extensively overlap.<p></p

Stability of %ES within sessions (A,B) and between sessions 1 and 2 (C,D).

<p>A. Difference in %ES for each participant between two runs of 200 trials within session 1 (calculated as Run 2-Run 1). Group mean±95% CI is shown for ESM and Norm groups. B. Correlation between %ES in Run 1 and Run 2. Least-squares linear regression line is shown with Pearson correlation coefficient and the p value for the correlation. Dotted horizontal and vertical lines show the 30% criterion level for defining a participant as an ESM, based on %ES from the two runs combined. C. Difference in %ES for each participant in Session 1 and Session 2. Other conventions are as in A. D. Correlation between %ES Session 1 and Session 2. Other conventions are as in B.</p

Overlap average latency distributions for ESMs and “normal” participants.

<p>Average (mean±95%CI) percentage latency distributions in overlap conditions for each group divided into Normal participants (Norm; A,C,E) and ESMs (B,D,F). Each panel also shows the number and percentage of each participant type within that group, the intersubject mean median latency (±SD), and the mean (±SD) percentage of express saccades.</p