Figure 20. The figure shows the reaction times of the errors (upper pane ls) and the distributions of the correction times (lower panels) of the same subjects as in Fig. 19.

fixation: the intrusive saccades, and the binocular instability of slow movemen ts of the two eyes in different directions or with different velocities. Now a third aspect is added by the occurrence of express saccades and in particular, when they occur as errors in the antisaccade task. Fixation may also by weak, when it does not allow to suppress the errors in the antisaccade task.

3.5. The Age Curves of Saccade Control

After these considerations and definitions we can look at the age development of the different variables. The data presented here contain many more subjects than in an earlier study, which has shown already the development of saccade control with age increasing from 7 to 70 years [Fischer et al. 1997].

Fig. 21 begins with the age curves of the performance of prosaccades with overlap conditions. The reaction times start with about 240 ms at the age of 7 to 8 years. During the next 10 years the reaction times become shorter by about 50 or 60 ms. From the age of 40 years one sees a gradual increase of the reaction times. At about 60 years they reach the level of the 7 year old children.

Figure 21. The diagrams show the age curves of the performance of prosaccades with overlap conditions. The left side depicts the age dependence of the reaction times, the right side shows the age dependence of the percentage of express saccades in the distributions. N=425.

One might expect that the occurrence of reflex-like movements (express saccades) is also a function of age, because the reflexes receive mor e cortical control with increasing age. However, this general aspect of the development may be seen much earlier in life, i.e. during the first year of life. Yet, there is strong tendency of a reduction of the number of express saccades with increasing age from a mean value just below 15% to a mean value of about 5%. There are however, extreme cases of subjects producing quite many express saccades. The large scatter in the data is due to these subjects.

It has been stated, that percentages of express saccades above a limit of 30% must be regarded as an exceptional weakness of the fixation system. T he corresponding subjects are called express saccade makers [Biscaldi et al. 1996]. An extreme case of an express saccade maker is shown in Fig. 22. In this subject the express saccades occur only to the right side.

Later in the book we will look at the percentage of express saccades among the prosaccades generated under overlap conditions, because we want to be pre-

Figure 22. The figure shows the distributions of saccadic reaction times fro m a single subject, who performed the prosaccade task with overlap condition. Saccades to the left side are depicted by the left panel, those to the right side by the right panel. Note the large peak of express saccade to the right as compared with no express saccades to the left.

pared for the diagnosis of saccade control in the following parts of the book, when large amounts of express saccades are made by single subjects of certain ages.

The Fig. 23 shows the age curves for the variables that describe the performance of the antisaccade task. The reaction times of the correct antisaccades are depicted by the upper left panel. The mean value of the youngest group at about 340 ms is 100 ms is slower than that of their prosaccades. As in the case of the prosaccades, a reduction of the reaction times is obtained within the next 10 years. However, they are reduced by about 100 ms. When compared with the prosaccades this reduction is two times as big.

The percentage of errors (middle left panel) reaches almost 80% for the youngest group. This means that they are almost completely unable to do the task in one step. The error rate decreases down to about 20%, stays at this level and increases after the age of about 40 years.

The bottom left panel depicts the correction rate. Out of the 80% errors, the youngest group was able to correct the primary error in only 40% of cases. The correction rate increases until the age of 20 to above 80%, stays at this level and decreases again after the age of 50 years.

Combining the two measures of error production and correction results in

Figure 23. The figure shows the age development of the performance of the antisaccade task with gap conditions. N=328. The period of the ”best” valu es is between 20 and 40 years of age.

the age curve of the percentage of uncorrected errors (misses) shown by the lower right panel of 23. The children of the youngest group reached the opposite