PSYC304 Vision Concepts

PSYC304 Vision

• Vision is an active, not passive process, the brain is not a hard drive and the eye is not a camera
• Numerous examples of active perceptual processing are described
• Visual information is processed in parallel, with separate systems in the retina
• Separate pathways carry visual information from the retina to the thalamus and cortex
• A receptive field is a region within the visual field that influences a neuron's activity, varying across the visual system
• Two theories of colour vision are discussed: they are not mutually exclusive but rather complementary, and do not completely describe colour perception on their own. Putative neural mechanisms for each and other factors influencing colour are described
• The visual cortex converts basic light stimuli into perceptions
• Visual information in the cortex follows separate pathways, with discrete damage to specific areas potentially affecting different aspects of visual processing.

Visual System: A Great Model for the CNS

• Introduction to vision, the retina, receptive fields, pathways to the cortex, visual perception, additional visual processing are covered
• Visual system is a great model for the CNS, which covers Introduction to vision, The retina, Receptive fields, Pathways to the cortex, Visual cortex, and Other visual processing.

Learning Objectives

• The brain and eye are not passive recorders, but active processors of information
• Numerous examples demonstrating active perceptual processing are provided
• Parallel processing in the visual system is described, along with the separate systems responsible for processing visual information in the retina
• The pathways for visual information are detailed, from the retina to the thalamus and finally to the cortex
• Definition and variations of receptive fields across the visual system.
• Two theories explaining colour vision are discussed
• The visual cortex's role in stimulus processing into perceptions is explained
• Separate pathways in the cortex responsible for processing visual information and their relationship to potential damage are explained

DARPA Grand Challenge 2004

• Computerized image capture of a driving vehicle, with accompanying image analysis to assist with navigation
• Self-driving vehicle attempts to be developed

First Self-Driving Car Fatality: 2018

• First instances of self-driving car accidents involving pedestrians are reported
• Cases of accidents involving self-driving cars and pedestrians are discussed

A Selective, Active Process

• Perception is an active process, not a passive recording of sensory input
• This process works by selecting, interpreting and influencing the world.

Reminder: Vision Has a Restricted Range

• Vision is based on evolutionary usefulness
• Vision varies by species
• Vision has a biological basis

Adaptation

• Vision is a result of constant stimulation
• Adaptation influences how the world is perceived in a personally useful way
• The need for constant eye movement is explained

The Retina

• The structure of the eye's retina is detailed
• The layers present in the retina are identified, enabling light to travel through

Reminder: A Less Messy Path to Travel

• Vertebrate and Octopus retina structures are compared
• Important retinal components are highlighted within the comparative diagrams

The Cornea and Lens Focus Images on Retina

• Diagrams explain normal vision, myopia and correction for myopia, showing how images are focused on the retina

A Well Organized Structure

• The layers and components of the retina are detailed and precisely described

Specialized Function

• The specialized components of photoreceptors within the retina, such as rods and cones, are defined

Rods and Cones Have Different Sensitivities of Wavelength

• The diagram illustrates the sensitivity differences between rods and cones in relation to different wavelengths of light

Most Mammals Have Dichromatic Colour Vision

• The differences between human and dog colour vision are highlighted

Colour Blindness in Humans

• Different types of colour blindness, such as protanopia, deuteranopia, tritanopia and achromatopsia are identified
• Examples of how these visually impaired individuals might understand the world are described

Acquired Trichromacy

• The brain's ability to interpret new information is highlighted
• Possible applications in therapeutic contexts are suggested

Parallel Processing, Convergence

• Convergence and parallel processing for rods and cones are contrasted
• The process involves many interconnected neurons in the retina

Pro's and Con's

• Pros and cons are outlined for both rods and cones separately
• Cones have high acuity and thus low sensitivity to light, while rods have high sensitivity and low acuity. Both are important to the visual system.

Lateral Inhibition and Mach Bands

• Contrast detection, not absolute values, is the core function of the visual system
• The centre-surrounding organization of receptive fields enhances contrast

Relative, not Absolute Values

• Centre-surround organization enhances perception of contrast
• Receptive fields are organized to highlight contrast, not absolute values

How to Measure Receptive Fields

• Receptive fields are measured to understand the region of the visual field that a neuron responds to
• Methods show how these fields can be identified

ON and OFF Channels

• Types of neuron channels called ON and OFF are described
• Measurements and experimental methods on visual stimuli affecting ON and OFF channels are highlighted

ON and OFF Channels via Lateral Inhibition

• Lateral inhibition is highlighted as the mechanism for ON and OFF channels, with a description of component parts
• The components of receptive fields are detailed

Lateral Inhibition in the Retina

• Lateral inhibition and receptive fields are related in a model of the retina, illustrating how neurons within the pathways communicate
• Different levels of illumination across the retina are visually shown.
• The rate at which receptors fire is illustrated

A Messy Path to Travel 2: The Revenge

• The structure of the eye, with particular reference to the retina and optic nerve, is presented
• Diagrams are provided as part of this description

Optic Nerve, Chiasm, Tract

• Diagram showing the optic nerve, chiasm and visual tracts is provided
• The details of the optic nerve, chiasm and visual pathways are visually identified

Cutting the Optic Chiasm

• Diagrams illustrate the cutting of the optic chiasm and the resulting effect on vision
• Symptoms resulting from an issue with the optic chiasm are explained

The Lateral Geniculate Nucleus (LGN)

• Diagram highlighting the different parts of the LGN
• Key details of LGN composition, such as the layers and their functions, are outlined

Specialized Processing

• Rod and cone types, bipolar cells, parvocellular and magnocellular layers, and their roles in handling visual information are outlined
• Details of the LGN, including layer types, are presented
• A mnemonic (P is for perception, and M is for motion) helps students remember which structure is for which task

Welcome to V1, the Primary Visual Cortex

• Primary visual cortex description, showing the role of Brodmann area 17
• Information from the LGN forms the crucial component of primary visual cortex

Retinotopic Map

• Diagrams illustrating the spatial arrangement of neurons in the visual cortex, known as the retinotopic map
• Cortical magnification is highlighted, emphasising that different regions need more resources in terms of space

Simple Cells

• How the experimental processes used to identify simple cells are described
• Diagrams showing identification of excitatory and inhibitory areas are provided

Ocular Dominance Columns

• The experimental method for identifying ocular dominance columns is outlined
• A diagram showing experimental setups

Orientation Columns

• Methods are provided for understanding how orientation columns are identified
• Diagrams illustrating orientations in a visual context along with the process

Colour Perception: Not Simply Wavelength

• Diagrams illustrate colour constancy aspects within the visual cortex

Theories of Colour

• Different theories for understanding colour perception are outlined

Theories of Colour

• Explanations of colour processing in two stages are provided
• Hering's opponent process theory is also introduced

Reminder: Perception Is Heavily Influenced by Top-Down Processes

• The influence of top-down processes on visual perception
• Diagrams provide perceptual constancy examples

Specialized Processing Continues!

• Diagrams highlight that specialized processing in the visual cortex continues within the visual cortex
• Dorsal and ventral stream processing, including the role of area V1, are discussed

Parallel Processing

• The processes within the visual cortex that help process visual information are detailed, including motion, form, depth, and colour
• A diagram illustrating information pathways for processing motion, form, depth, and colour are provided

Specialized Processing Continues

• Two pathways are described as specialized processing continues
• The pathways are the dorsal and ventral stream, both carrying important information

Cortical Damage May Not Affect All Vision

• Cortical damage might not affect all elements of the visual system. Certain aspects of vision are still present and can be identified
• Examples from Monkeys and Patient D.F. illustrate damaged regions of the brain affecting different aspects of vision in different ways

Other Visual Processing

• Non-conscious vision and issues related to such are highlighted
• Key findings are shown relating to non-conscious vision

Summary

• A short summary of the key elements of the visual system, such as active processes, relative rather than absolute values, and parallel processing, convergence and divergence is presented