Cueing the interpretation of a Necker Cube: a way to inspect fundamental cognitive processes

The term perceptual bistability refers to all those conditions in which an observer looks at an ambiguous stimulus that can have two or more distinct but equally reliable interpretations. In this work, we investigate perception of Necker Cube in which bistability consists of the possibility to interpret the cube depth in two different ways. We manipulated the cube ambiguity by darkening one of the cube faces (cue) to provide a clear cube interpretation due to the occlusion depth index. When the position of the cue is stationary the cube perceived perspective is steady and driven by the cue position. However, when we alternated in time the cue position (i.e. we changed the position of the darkened cube face) two different perceptual phenomena occurred: for low frequencies the cube perspective alternated in line with the position of the cue; however for high frequencies the cue was no longer able to bias the perception but it appears as a floating feature traveling across the solid with the cube whole perspective that returns to be bistable as in the conventional, bias-free, case.     

Cortical barrel lesions impair whisker-CS trace eyeblink conditioning

Whisker deflection is an effective conditioned stimulus (CS) for trace eyeblink conditioning that has been shown to induce a learning-specific expansion of whisker-related cortical barrels, suggesting that memory storage for an aspect of the trace association resides in barrel cortex. To examine the role of the barrel cortex in acquisition and retrieval of trace eyeblink associations, the barrel cortex was lesioned either prior to (acquisition group) or following (retention group) trace conditioning. The acquisition lesion group was unable to acquire the trace conditioned response, suggesting that the whisker barrel cortex is vital for learning trace eyeblink conditioning with whisker deflection as the CS. The retention lesion group exhibited a significant reduction in expression of the previously acquired conditioned response, suggesting that an aspect of the trace association may reside in barrel cortex. These results demonstrate that the barrel cortex is important for both acquisition and retention of whisker trace eyeblink conditioning. Furthermore, these results, along with prior anatomical whisker barrel analyses suggest that the barrel cortex is a site for long-term storage of whisker trace eyeblink associations.     

Pre-training to find a hidden platform in the Morris water maze can compensate for a deficit to find a cued platform in a rat model of Parkinson's disease

The bilateral intranigral infusion of 1 micromol 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in adult male Wistar rats caused a specific and partial loss of substantia nigra pars compacta (SNc) dopamine neurons, a partial depletion of striatal dopamine, and a deficit to learn the intra-maze cued version of the Morris water maze. Pre-training the SNc rats in the spatial version of the water maze or simply maintaining the animals on the water maze platform reversed this deficit. This improvement was even observed when the order of the extra-maze cues presented to the rats during pre-training of the spatial version was changed during training of the intra-maze cued version. However, this deficit was not reversed either by maintaining the animals on the platform if the spatial cues were surrounded and covered with a curtain or by swimming sessions in the maze without the escape platform and the curtain. These findings suggest that none of the following elements alone, learned during the spatial task pre-training, could help SNc rats learn the intra-maze cued task: improvement of swimming skills or knowledge of the existence of the escape platform; distance between the platform and the border of the pool; location of a particular extra-maze cue; relations among extra-maze cues. However, the simultaneous presence of the escape platform and extra-maze cues (irrespective of their relational configuration) during the pre-training sessions proved to be necessary for this improving effect to occur.     

Focusing attention on overlapping and non-overlapping figures with subjective contours

In a series of five experiments we investigated whether observers could focus attention on a restricted visual area that was demarcated by Kanizsa-like subjective contours, and whether this effect also occurred in the case of overlapping figures. The task was a simple reaction time to a luminance increment and the basic finding was that reaction time was faster when the imperative stimulus fell inside the focus of attention than when it fell outside. The first two experiments showed that the extent of the attentional focus could be adapted to a region that was demarcated by subjective contours, thus extending the results of previous studies that used regions demarcated by real contours. The last three experiments showed that, regardless of the type of margins, focusing was more efficient for the figure that was perceived as lying in front in a pair of overlapping figures. Received: 21 December 1999  / Accepted: 23 August 2000     

Racial phenotypicality bias in educational expectations for both male and female teenagers from different socioeconomic backgrounds

In three experiments (N = 56, 99, and 225), we showed that racial phenotypicality bias characterizes educational expectations for Chilean mestizo students: participants displayed more positive educational expectations for light complexioned than for dark complexioned high school students. In Study 1, with male high school target students, the relation between racial phenotypic appearance and educational expectations was mediated by differences in perceived competence. Study 2 suggests that the gender of the target student did not influence the occurrence of racial phenotypicality bias. Study 3 showed that racial phenotypicality bias occurs in both university students and high school teachers' judgements. Although socioeconomic background of the target student partially explained the effects of racial phenotypic appearance (especially in teachers), the latter exerted an additional and independent influence on educational expectations. These results underline the fact that effects of racial phenotypicality bias should not be overlooked in the educational domain. As mediational analyses suggested, these effects only partly occur because of stereotypical associations between racial phenotypic appearance and socioeconomic background, but also because of stereotypical associations between racial phenotypic appearance and attributed competence.