Implicit relational learning in a multiple-object tracking task.

We studied implicit relational learning by embedding contextual relational information into a multiple-object tracking task. In two experiments, participants were instructed to track two or four out of eight moving objects and report at the end of the trial whether a single cued object was among those they tracked (yes/no task). The stimulus display also contained two background strips of different width. In the informative condition, the location of the cued object predicted the correct choice: If the answer was "yes", then the cued object was always located next to the narrower strip; otherwise, it was always located next to the wider strip (or vice versa). In the random condition, the location of the object did not predict the correct choice. Participants in the informative condition consistently displayed lower tracking accuracy than in the random condition, possibly due to attentional demands introduced by implicit relational task. At the same time, participants in the informative condition demonstrated no awareness of the task structure; instead, their reports were consistent with the attempts to track moving objects. Our task can provide a suitable model for studying implicit relational learning in adult participants that is essential for establishing generality of factors affecting relational learning.

Figure-ground discrimination in the avian brain: the nucleus rotundus and its inhibitory complex.

In primates, neurons sensitive to figure-ground status are located in striate cortex (area V1) and extrastriate cortex (area V2). Although much is known about the anatomical structure and connectivity of the avian visual pathway, the functional organization of the avian brain remains largely unexplored. To pinpoint the areas associated with figure-ground segregation in the avian brain, we used a radioactively labeled glucose analog to compare differences in glucose uptake after figure-ground, color, and shape discriminations. We also included a control group that received food on a variable-interval schedule, but was not required to learn a visual discrimination. Although the discrimination task depended on group assignment, the stimulus displays were identical for all three experimental groups, ensuring that all animals were exposed to the same visual input. Our analysis concentrated on the primary thalamic nucleus associated with visual processing, the nucleus rotundus (Rt), and two nuclei providing regulatory feedback, the pretectum (PT) and the nucleus subpretectalis/interstitio-pretecto-subpretectalis complex (SP/IPS). We found that figure-ground discrimination was associated with strong and nonlateralized activity of Rt and SP/IPS, whereas color discrimination produced strong and lateralized activation in Rt alone. Shape discrimination was associated with lower activity of Rt than in the control group. Taken together, our results suggest that figure-ground discrimination is associated with Rt and that SP/IPS may be a main source of inhibitory control. Thus, figure-ground segregation in the avian brain may occur earlier than in the primate brain.