L10_Low_Level_Sensory_Perception_Annotated

Lecture Overview

• Lecture Title: Low Level Sensory Perception

• Course: PSC 101 - Bio Psych

• Date: February 13th, 2025

Introduction to Visual Perception

• Group Discussion Activity:

  • Think for 1 minute about how you see a smiley face.

  • Pair up with a neighbor and share thoughts.

Learning Objectives

• 10.1 Describe how specialized receptors in the eye can represent light as neural activity.

• 10.2 Illustrate how an image from the outside world can be encoded by the retina to form a retinotopic map.

• 10.3 Draw the neural connections visual information follows from the eye to the primary visual cortex.

• 10.4 Explain how visual information is organized in the primary visual cortex.

Sensory Systems Overview

• Information Acquisition:

  • Our brains do not directly obtain sensory information but rely on nervous system networks.

  • The systems process various sensory modalities like sight, touch, hearing, and smell.

• Visual System Focus:

  • While we'll focus on sight, principles learned can be applied to other senses.

Specialized Receptors

• Each sensory system has specialized receptors that encode physical environmental features as changes in membrane potentials.

• Characteristics of Specialized Receptors:

  • Neurons with structural modifications best responding to specific external stimuli.

  • Unique to each sensory system with different forms of processed information.

Photoreceptors in the Visual System

• Function:

  • Photoreceptors are specialized receptors that act as light sensors, converting photons into electrochemical signals.

• Photon Characteristics:

  • Photons are packets of light.

  • Brightness is determined by the number of photons, and color is determined by photon wavelength.

Mechanism of Action

• Structure of Photoreceptors:

  • Contain disks with rhodopsin proteins activated by photons.

  • G proteins are activated, leading to changes in membrane potential.

• Types of Photoreceptors:

  • Rods: Respond to low-light environments, provide low-resolution and non-color vision.

  • Cones: Function in well-lit conditions, provide high-resolution and color vision.

Rods vs. Cones

• Rods:

  • More disks than cones to capture photons, effective in low light.

  • Results in compromises in resolution and color vision.

• Cones:

  • Have fewer disks than rods and require more photons to activate.

  • Three types respond to specific colors: Short (blue), Medium (green), and Long (red).

Cone Activity and Color Blindness

• Population Coding:

  • Cone types work together to accurately represent complex colors, enhancing color perception.

• Color Blindness:

  • Malfunctions in one or more cone types lead to conditions like red-green color blindness.

The Retina

• Structure:

  • Contains over 100 million photoreceptors and encodes visual information indexed in a retinotopic map.

• Flow of Information:

  • Photons pass through layers of cells, activating the photoreceptors which communicate with bipolar and retinal ganglion cells (RGCs) to send information to the brain.

Visual Pathway to the Brain

• Pathway Description:

  • Information from photoreceptors travels through bipolar cells to RGCs, forming the optic nerve containing retinotopic organization.

  • At the optic chiasm, information from each eye is combined, forming left and right visual fields.

  • The optic tracts transmit visual information to the lateral geniculate nucleus of the thalamus, and subsequently to the primary visual cortex (V1).

Primary Visual Cortex (V1)

• Function:

  • V1 processes initial visual information and is located in the occipital lobe.

  • Each hemisphere of V1 processes information from the opposite visual field.

• Column Structure:

  • V1 consists of interconnected columns corresponding to points on the retina, forming a retinotopic map.

  • Columns combine signals from rods and cones, processing light intensity, color, and movement.

Summary of Visual Functionality

• Seeing the Smiley Face:

  • Light from a screen travels to the retina, where action potentials carry the information to the brain, processed by V1 columns to interpret edges, color, and intensity, resulting in the perception of a smiley face.

Learning Objectives for Low Level Sensory Perception

10.1 Describe how specialized receptors in the eye can represent light as neural activity.

Specialized receptors in the eye, primarily photoreceptors known as rods and cones, are responsible for detecting light and converting it into neural signals. When photons, or light particles, hit these receptors, they induce a change in membrane potential due to the activation of proteins like rhodopsin in rods or photopsins in cones. These changes result in graded potentials, which can lead to the generation of action potentials that are transmitted through the optic nerve to the brain, allowing for the perception of light.

10.2 Illustrate how an image from the outside world can be encoded by the retina to form a retinotopic map.

The retina encodes visual images through a process called retinotopic mapping. As light enters the eye and is focused on the retina, each photoreceptor responds to specific light patterns. The spatial arrangement of these receptors corresponds to the spatial layout of the visual field, creating a retinotopic organization where adjacent areas of the retina represent adjacent areas of the visual field. This structured mapping is crucial for accurately conveying visual information to the brain.

10.3 Draw the neural connections visual information follows from the eye to the primary visual cortex.

Visual information travels from the eye through a series of neural connections: 1) Photoreceptors (rods and cones) receive light stimuli and convert them into electrical signals. 2) These signals are relayed to bipolar cells, which process and transmit information to retinal ganglion cells (RGCs). 3) RGCs aggregate the information and form the optic nerve, which exits the eye. 4) At the optic chiasm, the visual information is partially crossed so that signals from the left visual field are processed in the right hemisphere and vice versa. 5) The signals are then sent through the optic tracts to the lateral geniculate nucleus (LGN) of the thalamus, which acts as a relay station before transmitting the information to the primary visual cortex (V1) in the occipital lobe.

10.4 Explain how visual information is organized in the primary visual cortex.

In the primary visual cortex (V1), visual information is organized into columns that correspond to specific points on the retina, maintaining the retinotopic map. Each column processes different aspects of the visual scene, including light intensity, color, and movement, by integrating signals from both rods and cones. The columns are interconnected and work together to form a coherent perception of the visual environment. Additionally, the functionality of V1 allows for the differentiation of visual stimuli, aiding in the perception of contours, shapes, and motion as visual elements, such as a smiley face, are recognized and interpreted by the brain.