André Frazão Helene

A construção da atenção a partir da memória

The processes that lead to the selection of information for additional processing, which characterizes attention, depend upon previous experiences and expectancies generated in the light of stored past experiences regularities and plans for action. It is proposed that conceptual association between memory and attention brings advantages for explaining a diversity of attentional phenomena and allow to generate testable predictions relating past experiences and performance in tests for attention. A model is presented relating the trained neural network (memories) and attention during performance of behavioral tasks.

Ants Can Learn to Forage on One-Way Trails

The trails formed by many ant species between nest and food source are two-way roads on which outgoing and returning workers meet and touch each other all along. The way to get back home, after grasping a food load, is to take the same route on which they have arrived from the nest. In many species such trails are chemically marked by pheromones providing orientation cues for the ants to find their way. Other species rely on their vision and use landmarks as cues. We have developed a method to stop foraging ants from shuttling on two-way trails. The only way to forage is to take two separate roads, as they cannot go back on their steps after arriving at the food or at the nest. The condition qualifies as a problem because all their orientation cues – chemical, visual or any other - are disrupted, as all of them cannot but lead the ants back to the route on which they arrived. We have found that workers of the leaf-cutting ant Atta sexdens rubropilosa can solve the problem. They could not only find the alternative way, but also used the unidirectional traffic system to forage effectively. We suggest that their ability is an evolutionary consequence of the need to deal with environmental irregularities that cannot be negotiated by means of excessively stereotyped behavior, and that it is but an example of a widespread phenomenon. We also suggest that our method can be adapted to other species, invertebrate and vertebrate, in the study of orientation, memory, perception, learning and communication.

Parkinson’s Disease Progression: Implicit Acquisition, Cognitive and Motor Impairments, and Medication Effects

Parkinson’s disease (PD) symptoms have been collectively ascribed to malfunctioning of dopamine-related nigro-striatal and cortico-striatal loops. However, some doubts about this proposition are raised by controversies about the temporal progression of the impairments, and whether they are concomitant or not. The present study consists of a systematic revision of literature data on both functional PD impairments and dopaminergic medication effects in order to draw a coherent picture about the disease progression. It was done in terms of an explanatory model for the disruption of implicit knowledge acquisition, motor and cognitive impairments, and the effects of dopaminergic medication on these functions. Cognitive impairments arise at early stages of PD and stabilizes while disruption of implicit knowledge acquisition and motor impairments, are still in progression; additionally, dopaminergic medication reduces motor impairments and increases disruption of implicit knowledge acquisition. Since this model revealed consistency and plausibility when confronted with data of others studies not included in model’s formulation, it may turn out to be a useful tool for understanding the multifaceted characteristics of PD.

Training of direct ophthalmoscopy using models

The time spent on ophthalmology training in medical schools has reduced over the last decades, and the number of doctors unable to solve the most basic ophthalmic problems has increased.

On Sequence Learning Models: Open-loop Control Not Strictly Guided by Hick's Law

According to the Hick’s law, reaction times increase linearly with the uncertainty of target stimuli. We tested the generality of this law by measuring reaction times in a human sequence learning protocol involving serial target locations which differed in transition probability and global entropy. Our results showed that sigmoid functions better describe the relationship between reaction times and uncertainty when compared to linear functions. Sequence predictability was estimated by distinct statistical predictors: conditional probability, conditional entropy, joint probability and joint entropy measures. Conditional predictors relate to closed-loop control models describing that performance is guided by on-line access to past sequence structure to predict next location. Differently, joint predictors relate to open-loop control models assuming global access of sequence structure, requiring no constant monitoring. We tested which of these predictors better describe performance on the sequence learning protocol. Results suggest that joint predictors are more accurate than conditional predictors to track performance. In conclusion, sequence learning is better described as an open-loop process which is not precisely predicted by Hick’s law.

Alguns aspectos da óptica do olho humano

This paper describes some aspects of the human eye adopting a progressive approach. We begin studying a simple visual system to which we progressively include the other eye components. Initially, the human eye is represented by a simple void sphere with a hole through which the light passes and strikes the opposite surface where is the retina. However, this simple model does not produce a sharp image on the retina. In order to improve the image quality, the sphere is filled with a material with a refractive index equal to that of the substances that fill the eye (vitreous and aqueous humors). The image formed in the retina becomes less blurred, but not completely sharp. After that, we study the role of the cornea to the improvement of the image quality. But the cornea does not ensure a perfect image. The next step is to study the role of the lens. The adopted approach is more or less similar to the evolutionary history of the eye during the last 500 million years, from a simple photosensitive sheet to the complex vertebrate eyes. Calculations are performed using the basic equations of the geometric optics. Finally, we present a model of the human eye made with transparent spheres which allows us to explore some aspects of the human vision.

Goalkeeper Game: A new assessment instrument in neurology showed higher predictive power than MoCA for gait performance in people with parkinson\'s disease

Objective To investigate the use of the Goalkeeper Game (GG) to assess gait automaticity decline under dual task conditions in people with Parkinson’s disease (PPD) and compare its predictive power with the one of the MoCA test. Materials and Methods 74 PPD (H&Y stages: 23 in stage 1; 31 in stage 2; 20 in stage 3), without dementia (MoCA cut-off 23), tested in ON period with dopaminergic medication were submitted to single individual cognitive/motor evaluation sessions. The tests applied were: MoCA, GG, dynamic gait index (DGI) task and timed up and go test (TUG) under single and dual-task (DT) conditions. GG test resulted in 9 measures extracted via a statistical model. The predictive power of the GG measures and the MoCA score with respect to gait performance, as assessed by DGI and DT-TUG, were compared. Results The predictive models based on GG measures and MoCA score obtained, respectively, sensitivities of 65% and 56% for DGI scores and 59% and 57% for DT-TUG cost at a 50% specificity. GG application proved to be feasible and aroused more motivation in PPDs than MoCa. Conclusion GG, a friendly and ludic game, was able to reach a good power of gait performance prediction in people at initial and intermediate stages of PD evolution.