Attentional control in learning to discriminate bars and gratings.

Transfer effects of learning a spatial-frequency and a bar-width discrimination task on the performance in three other discrimination tasks (relative bar position, local width, and global-size discrimination) have been investigated. In the spatial-frequency discrimination learning task, subjects were trained with grating stimuli which varied in spatial frequency, relative bar position, and grating patch size, but only spatial frequency was relevant for discrimination. The bar-width discrimination learners had to judge the width of single grating bars appearing at random positions distributed around a display center. During the course of 10 consecutive days, all subjects showed a significant reduction of discrimination thresholds. Regarding learning transfer, we find that practicing the spatial-frequency discrimination task yields quite strong improvement of bar-width discrimination and, vice versa, learning bar-width discrimination also leads to strong improvement of spatial-frequency discrimination performance, indicating involvement of coding pathways which are shared by both tasks. On the other hand, there is no performance improvement when subjects do different tasks (grating patch size and relative bar position discrimination) with the same stimulus material as the learning stimuli. The finding of task-driven selective learning for only one local stimulus attribute among other local and global attributes shows that feature-based attentional preselection of basic stimulus attributes is involved in learning. Moreover, differential learning effects for two different local stimulus features indicate that, governed by top-down control, different neural pathways starting from the same low-level code base may be formed in the course of discrimination training.