Bayesian Strategy in Image Formation

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Questions and Answers

What do prior probability distributions in Bayesian strategy typically represent?

Knowledge of spatial frequency tuning

Knowledge of image formation through projection on the retina

Knowledge of object shapes, constituent materials, and illumination (correct)

Knowledge of visual scene processing

What type of visual processing is concerned with determining which boundaries and surfaces belong to specific objects and which are part of the background?

Low-level visual processing

Object recognition processing

High-level visual processing

Intermediate-level visual processing (correct)

What is a characteristic of all neurons in vision?

Spatial frequency tuning

Visual scene processing

Receptive field (correct)

Object recognition

What determines the neuron's spatial frequency tuning?

The size of the receptive field Signup and view all the answers

How do perceptions of ambiguous images change compared to non-ambiguous images?

They are more influenced by prior knowledge Signup and view all the answers

What is an example of prior knowledge in object perception?

Solids are more likely to be convex than concave Signup and view all the answers

What changes with eccentricity in the cortex?

The amount of cortex devoted to one degree of viewing angle Signup and view all the answers

What allows the population of neurons to resolve two nearby locations even though a single neuron cannot?

The different RF profiles of the neurons Signup and view all the answers

What is the main reason for dedicating more cortical space to the central part of the visual field?

Because the visual system has the highest spatial resolution in this area Signup and view all the answers

What happens to the firing rate of ON-center ganglion cells when the dark stimulus disappears?

It increases Signup and view all the answers

What is the organization of the receptive field in retinal ganglion cells?

Two concentric circular areas with opposite and antagonistic response Signup and view all the answers

What happens when the center and surround of the receptive field are illuminated simultaneously in an ON-center cell?

The discharge frequency does not change Signup and view all the answers

What is the spatial frequency range at which sensitivity is greatest in humans for sinusoidal gratings?

5-8 cycles / visual degree Signup and view all the answers

What happens to sensitivity for spatial frequencies above 30-50 cycles / degree?

It is attenuated Signup and view all the answers

What is the effect of illumination on the central part of the receptive field in an OFF-center cell?

Inhibitory response Signup and view all the answers

What is the mechanism responsible for the inhibitory response in the surrounding part of the receptive field in ON-center cells?

Lateral inhibition Signup and view all the answers

What is the absolute threshold of contrast sensitivity at high spatial frequencies?

50 cycles per degree Signup and view all the answers

What is the main reason for the decline in sensitivity at low spatial frequencies?

Inhibitory and antagonistic action of the periphery Signup and view all the answers

What is the characteristic of the visual system in terms of spatial frequencies?

Band-pass behavior Signup and view all the answers

At which spatial frequency are gratings most visible?

5 cycles per degree Signup and view all the answers

What is the characteristic of neurons in area V1 in terms of their receptive fields?

Elongated and respond to a narrow range of orientations Signup and view all the answers

What is the main function of the selectivity of neurons in area V1?

To analyze the shape of an object Signup and view all the answers

What is the range of spatial frequencies that humans are most sensitive to?

4-6 cycles per degree Signup and view all the answers

What is the relationship between stimulus contrast and visibility in the figure?

The central bars are visible even at low contrast Signup and view all the answers

What is one potential advantage of cortical columnar segregation?

Minimization of connection lengths and processing time Signup and view all the answers

Which pathway is primarily involved in object recognition?

Ventral pathway Signup and view all the answers

What is the primary function of the dorsal pathway?

Stimulus movement information Signup and view all the answers

What is a characteristic of connections between cortical areas?

Reciprocal connections Signup and view all the answers

Where is V4 located in the macaque monkey?

Prelunate gyrus and in the depths of the lunate and superior temporal sulci Signup and view all the answers

Why is identification more difficult for human vision compared to categorization?

Identification requires more neural processing Signup and view all the answers

What is a category in the context of visual perception?

A set of objects or events treated equivalently Signup and view all the answers

What is the primary difference between how computer vision and human vision approach object identification?

Computer vision can easily identify objects, but human vision finds it more difficult Signup and view all the answers

What is the shape of the receptive fields of LGN cells in the monkey?

Non-oriented circular Signup and view all the answers

What type of stimuli do simple cells respond well to?

Sinusoidal gratings (Gabor patches) Signup and view all the answers

What is a characteristic of complex cells in terms of their receptive fields?

They respond similarly to light or dark stimuli in all positions Signup and view all the answers

What is the purpose of end-stopped cells in visual processing?

To detect angles or curved lines Signup and view all the answers

What is the effect of a long straight line on an end-stopped cell?

It cancels the excitatory response with inhibitory effect Signup and view all the answers

How do complex receptive fields arise according to the hierarchical model?

From the convergence of simple cells with similar orientation preferences Signup and view all the answers

What is the orientation of the ON and OFF regions of the receptive field in an end-stopped cell?

The same orientation (e.g. vertical) Signup and view all the answers

What is the effect of a stimulus that extends beyond a specific portion of the receptive field on an end-stopped cell?

It reduces the response of the cell Signup and view all the answers

Study Notes

Prior Probability Distributions and Visual Perception

Prior probability distributions represent knowledge of object shapes, constituent materials, and illumination, influencing visual perception.
Likelihood distributions represent knowledge of how images are formed through projection on the retina.
Prior knowledge is more influential in yielding a non-ambiguous percept when the image is ambiguous.
Perceptions can be either data-driven or prior knowledge-driven.

Intermediate-Level Visual Processing

Intermediate-level visual processing determines which boundaries and surfaces belong to specific objects and which are part of the background.
Visual scenes comprise many thousands of line segments and local surface patches.

Receptive Field (RF)

The concept of RF was introduced by Charles Sherrington in 1906.
RF is a characteristic of all neurons, indicating the region of the visual scene where the stimulus must fall to excite or inhibit the neuron.
The size of the RF determines the neuron's spatial frequency tuning, with smaller RFs resolving higher spatial frequencies.
Cortical space devoted to one degree of viewing angle changes with eccentricity, with more space dedicated to the central part of the visual field.

ON-Center and OFF-Center Ganglion Cells

ON-Center ganglion cells are excited by a light stimulus in the center of the receptive field.
OFF-Center ganglion cells are excited by a dark stimulus in the center of the receptive field.
The firing rate of ON-center ganglion cells increases soon after the dark stimulus disappears, and vice versa for OFF-center ganglion cells.

Retinal Ganglion Cells and Lateral Inhibition

Retinal ganglion cells have an organization of the receptive field with two concentric circular areas with opposite and antagonistic responses.
ON-center cells have an excitatory response in the center and an inhibitory response in the surround, while OFF-center cells have the opposite response.
Lateral inhibition occurs when the illumination of the surround causes an inhibitory response.

Spatial Frequency and Grating Stimuli

In humans, sensitivity is greatest for spatial frequencies around 5-8 cycles per degree.
Contrast sensitivity declines sharply at high spatial frequencies and declines at low spatial frequencies.
The visual system has band-pass behavior, rejecting all but a narrow band of spatial frequencies.
Gratings with a frequency of about 5 cycles per degree are the most visible.

Neurons in Area V1

Neurons in area V1 are classically divided into two types: simple and complex (Hubel and Wiesel, 1959).
Simple cells have elongated RFs, respond to a narrow range of orientations, and have an orientation tuning curve.
Complex cells are less selective for the position of the stimulus in the receptive field, respond similarly to light and dark stimuli, and are activated by linear stimuli crossing their receptive fields in one direction.

End-Stopped Cells

End-stopped cells respond better to linear stimuli of a certain length or with an end that does not extend beyond a specific portion of the cell's receptive field.
End-stopped cells may serve to detect angles or curved lines of visual images.

Hierarchical Model

The hierarchical model (Hubel and Wiesel, 1962) suggests that simple cell receptive fields are constructed from the convergence of geniculate inputs with receptive fields aligned in the visual space.
Complex receptive fields arise from the convergence of simple cells with similar orientation preferences.

Cortical Columns and Dorsal and Ventral Pathways

Cortical columns may minimize connection lengths and processing time, which could be evolutionarily important.
The dorsal and ventral pathways are highly interconnected, sharing information and enabling the perception of object shape.
Reciprocity is an important feature of connectivity between cortical areas.

Area V4

In the macaque monkey, V4 is located on the prelunate gyrus and in the depths of the lunate and superior temporal sulci, extending to the surface of the temporal-occipital gyrus.

Categorization and Object Recognition

Categorization occurs when distinct objects or events are treated equivalently, such as when labeled with the same name or responded to with the same action.
Although stimuli are distinct, organisms do not treat them uniquely, but respond based on past experience and categorization.

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Description

This quiz is about the Bayesian strategy in image formation, including prior probability distributions and likelihood distributions. It involves knowledge of object shapes, materials, and illumination.