Bayesian Strategy in Image Formation

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.