Show Tag: top-down

Select Other Tags

Gottlieb et al. found that the most salient and the most task-relevant visual stimuli evoke the greatest response in LIP.

Lee and Mumford interpret the visual pathway in terms of Bayesian belief propagation: each stage in the processing uses output from the one further up as contextual information and output from the one further down as evidence to update its belief and corresponding output.

Each layer thus calculates probabilities of features of the visual display given noisy and ambiguous input.

Kastner and Ungerleider propose that the top-down signals which lead to the effects of visual attention originate from brain regions outside the visual cortex.

Regions lesions of which can induce visuospatial neglect include

  • the parietal lobe, in particular the inferior part,
  • temporo-parietal junction,
  • the anterior cingulate cortex,
  • basal ganglia,
  • thalamus,
  • the pulvinar nucleus.

Spatial attention can enhance the activity of SC neurons whose receptive fields overlap the attended region

Verschure summarizes version VII of his distributed adaptive control model as "a unifying theory" of perception cognition, and action. He states that it uses a learned world model in its contextual layer which biases perception processing (top-down) on the one hand, and saliency (bottom-up) on the other. Between these to appears to be what he calls the validation gate which defines matching and mismatch between world model and percepts.

Goldberg and Wurtz found that neurons in the superficial SC respond more vigorously to visual stimuli in their receptive field if the current task is to make a saccade to the stimuli.

Responses of superficial SC neurons do not depend solely to intrinsic stimulus properties.

Neurons that receive auditory and visual ascending input also receive (only) auditory and visual descending projections.

Deco and Rolls introduce a system that uses a trace learning rule to learn recognition of more and more complex visual features in successive layers of a neural architecture. In each layer, the specificity of the features increases together with the receptive fields of neurons until the receptive fields span most of the visual range and the features actually code for objects. This model thus is a model of the development of object-based attention.

Yu and Dayan argue that uncertainty should suppress top-down, context-dependent factors in inference, and strengthen learning about the situation.

The cognitivist interpretation of the terms 'bottom-up' and 'top-down' is that of hypothesis-driven or expectation-driven processing., respectively.

The anatomical interpretation of the terms 'bottom-up' and 'top-down' is that of feedforward vs. feedback connections in a processing hierarchy, respectively.

The terms 'bottom-up' and 'top-down' can mean different, related things depending on context. Engel et al. list four:

  • anatomical
  • cognitivist
  • gestaltist
  • (neural) dynamicist

Grossberg's ART and Friston's theory of cortical responses appeal to the anatomical interpretation of 'top-down' and 'bottom-up' processing and stress feedback as well as feedforward connections.

According to the temporal binding theory, top-down control is realized by top-down influences on synchronization and oscillations in activity. Engel et al. call this model of top-down control the `dynamicist' notion.

Saccade targets tend to be the centers of objects.

Both populations in prefrontal cortex and posterior parietal cortex show correlates of bottom-up and top-down visual attention.

Visual attention is influenced both by local and global saliency, ie. bottom-up processes, and by semantics, ie. top-down processes.

The biased competition theory of visual attention explains attention as the effect of low-level stimuli competing with each other for resources—representation and processing. According to this theory, higher-level processes/brain regions bias this competition.

Much of the activity of cognitive systems is not only due to current stimuli, but also to a large degree to previous experience, specifically due to the expectations following from it.

A precondition for intelligence is the ability to use previous experience to abstract away from current stimulus conditions—to use both information from current sensory input and from past experience and potentially discard one for the other.

Top-down processing is necessary in order to be able to mix current information from sensory input with previous experience.

Many recent neural theories assume that higher-level brain regions form hypotheses about the world and that top-down, or feedback connections carry predictions for low-level stimuli derived from these hypotheses.

Early theories which assume that higher-level brain regions form hypotheses about the world and that top-down, or feedback connections carry predictions for low-level stimuli derived from these hypotheses is Grossberg's ART.