Visual Perception: Receptive Fields and Ganglion Cells

Receptive Fields and Visual Processing

• The central part of the visual field has smaller and densely packed receptive fields, resulting in higher spatial resolution.
• ON-center ganglion cells are excited by light stimuli in the center of the receptive field, while OFF-center ganglion cells are excited by dark stimuli in the center.
• The firing rate of ON-center ganglion cells increases when the dark stimulus disappears, and similarly, the discharge rate of OFF-center ganglion cells increases when the light stimulus disappears.
• Retinal ganglion cells have a concentric circular organization of receptive fields with opposite and antagonistic responses.
• ON-center cells have an excitatory response to central illumination and an inhibitory response to surrounding illumination, while OFF-center cells have the opposite response.

Spatial Frequencies and Visual Sensitivity

• Humans have greater sensitivity to spatial frequencies around 5-8 cycles/visual degree, and sensitivity declines for higher and lower frequencies.
• The visual system has band-pass behavior, rejecting all but a narrow band of spatial frequencies.
• Gratings with a frequency of approximately 5 cycles/degree are the most visible.
• The visual system is more sensitive to an intermediate range of spatial frequencies (about 4-6 cycles/degree) and less sensitive to both lower and higher space frequencies.

Neurons in Area V1

• Neurons in area V1 are divided into two types: simple and complex.
• Simple cells respond to a narrow range of orientations and have elongated receptive fields.
• Complex cells are less selective for position and respond similarly to light and dark stimuli in all positions of the receptive field.
• Complex cells respond well 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.

Hierarchical Model of Visual Processing

• According to the hierarchical model, simple cell receptive fields are constructed from the convergence of geniculate inputs with receptive fields aligned in visual space.
• Complex receptive fields arise from the convergence of simple cells with similar orientation preferences.

Cortical Columns and Visual Processing

• Cortical columns are thought to minimize connection lengths and processing time, which could be evolutionarily important.
• The dorsal and ventral pathways are highly interconnected, sharing information and contributing to object recognition through kinematic cues.

Object Recognition and Categorization

• Categorization is the process of treating distinct objects or events equivalently, and is a fundamental function of living beings.
• Object recognition involves integration of visual features extracted at earlier stages in the visual pathways, and incorporates information from other sensory modalities and emotional valence.
• Area V1, V2, and V4 are located in the occipital lobe, while area TEO and IT are located in the temporal lobe.
• IT neurons have relative selectivity for complex objects, which appears somewhat arbitrary.

Learn about the organization of visual perception, including the structure of receptive fields and the roles of ON-Center and OFF-Center ganglion cells in processing light and dark stimuli.