Sensory Functions and Emotional Development

Sensory Functions Overview

• Traditionally, we recognize five sensory functions: Taste, Smell, Hearing, Touch, and Vision.

• Additionally, we will discuss Proprioception and the Vestibular system.

• While taste is relevant to eating and auditory processing is a specialty for some Occupational Therapists (OTs), today's focus will be on visual perception, touch, vestibular, and proprioception, and their impact on occupation.

Visual Perception

The Optic Tract

• The optic tract is an extension of the optic nerve.

• Crossing of Optic Nerves: Only about half of the optic nerve fibers cross over at the optic chiasm.

  • Fibers from the right side of both eyes (the right visual field from each eye) cross over to the right side of the brain (the visual cortex).

  • Fibers from the left side of both eyes (the left visual field from each eye) stay on the left side of the brain (the visual cortex).

• Hemianopsia: Damage to one of the optic tracts results in hemianopsia, characterized by blank spots in the visual field. For instance, damage to the right optic tract would cause blind spots in the right visual field of each eye.

  • Clinical Example: A brain tumor in the pituitary gland, which is located near the optic chiasm, can cause hemianopsia, affecting central vision as well.

Visual Development Timeline in Infants

• Infant sight develops at varying rates, but a general timeline exists:

  • Newborns: Primarily rely on side (peripheral) vision; central vision is not yet strong. Can spot things directly beside them.

  • Within $2$ weeks: May begin to notice light and dark shapes, and be drawn to bright colors and large shapes.

  • About $1$ month: May start to focus on a parent's face for short periods. Still mostly interested in close-by objects.

  • Between $2$ and $4$ months: Eyes start to follow and focus on moving objects.

  • Months $5$ through $8$: Begin to recognize parents' faces at a distance. Depth perception (the ability to notice how far things are) starts to improve. Colors may appear more vibrant.

  • Months $9$ through $12$: Depth perception becomes refined enough for fine motor tasks like grabbing objects between the thumb and forefinger (pincer grasp).

• Practical Application: This developmental understanding explains why high-contrast, black and white visual stimuli are often recommended for infants to support visual development.

Ocular Motor System

This system describes how the eyes move and process visual information:

• Fixation: The ability to hold the eyes steadily on a stationary object.

• Acuity: The sharpness of vision, often tested as $20/20$ vision.

• Pursuits (Tracking): The ability to maintain fixation on a moving object.

• Saccades: Rapid changes in eye fixation, like when reading across a line of text.

• Accommodation: The ability of each eye to adjust its focus to compensate for blurred images at different distances (e.g., looking from a close object to a far object and back).

• Binocular Fusion: Combining two images, one from each eye, into a single, cohesive image, which contributes to depth perception.

• Convergence and Divergence: The eyes moving inward (converging) or outward (diverging) to track objects at different distances (e.g., looking down at a computer and then up again).

Visual Perceptual Skills

These are cognitive skills that allow us to interpret and understand visual information:

• Visual Attention: The ability to select relevant visual input and allocate sufficient time for the eyes and brain to process an object.

• Visual Memory: The ability to recall visual information after it has been presented.

• Form Constancy: Recognizing that the shape or form of an object remains the same regardless of its orientation, size, or format (e.g., identifying different fonts of the letter 'A' or rotated triangles).

• Visual Closure: The ability to recognize an object even when parts of it are hidden or incomplete (e.g., knowing what is on a screen even if someone's head is partially blocking it).

• Figure Ground: The ability to distinguish an object (figure) from its background (ground) (e.g., finding a specific piece of clothing in a cluttered closet, finding a fork in a drawer, finding matching socks).

• Position in Space: Understanding the location and orientation of objects relative to oneself or other objects (e.g., identifying which way an arrow is pointing, having kindergarteners line up facing a specific direction).

Tactile System

• The tactile system has two main functions:

  • Protective: Detects sensations like pain, temperature, and potentially harmful stimuli.

  • Discriminative: Differentiates between various textures, shapes, and pressures, allowing for fine motor tasks and object recognition by touch.

• Reactivity Levels:

  • Hyperreactive (Tactile Defensiveness): An over-responsiveness to touch, where light touch or certain textures can be perceived as irritating or overwhelming (e.g., a child refusing to touch glue or specific art materials).

  • Hyporeactive (Under-responsive/Sensory Seeking): An under-responsiveness to touch, where individuals seek out more tactile input (e.g., a child constantly touching everything around them).

• Support for Occupations:

  • Activities of Daily Living (ADLs): Discriminative touch helps with tasks like dressing (e.g., feeling for a button rather than a clock, buttoning clothes).

  • Play: Enables interaction with different textured toys. In board games, it allows manipulation of game pieces without visual input.

  • Social Participation: Influences comfort with physical contact, such as touching someone during a friendly interaction.

Proprioception

• Proprioception is the sense of the relative position of one's own body parts and strength of effort being used in movement. It provides awareness of body position in space without relying on vision.

• Three Key Components:

  • Muscle Spindles: Detect the length or stretch of muscles.

  • Golgi Tendon Organs: Detect the tension in tendons, indicating the force applied by muscles.

  • Joint Receptors: Detect pressure within joints, indicating joint position and movement.

• Mechanism: When the arm bends, muscle spindles in the bicep detect shortening, while golgi tendons and joint receptors detect tension and pressure. This continuous feedback allows the brain to know the arm's position and the force being exerted (e.g., the weight of an object being held).

• Examples in Occupations:

  • Driving: Knowing the location of the gas and brake pedals without looking. Modulating pressure on the brake pedal based on the situation (e.g., a sudden stop versus gradual slowing).

  • Cooking: Pouring the correct amount of olive oil by sensing the flow rate, opening a jar by applying appropriate force, cracking an egg with the right amount of force (e.g., an ostrich egg versus a quail egg).

  • Tool Use: Adjusting grip and force when using tools.

  • Dressing: Manipulating clothing fasteners or adjusting clothing without looking.

  • Social Interactions: Avoiding bumping into people, regulating the force of a hug to be appropriate and comfortable for others.

Vestibular System

• The vestibular system provides the brain with information about motion, head position, and spatial orientation. It is crucial for balance, stabilizing the head and body during movement, and maintaining posture.

• Main Components in the Inner Ear:

  • Vestibular Labyrinth: Continuous with the cochlea.

  • Semicircular Canals (3 tubes): Detect rotational head movements (nodding up/down, shaking side-to-side, tilting left/right). They are filled with endolymph (fluid). Movement of endolymph displaces hair cells within the ampulla of each canal, sending signals to the brain.

  • Otolith Organs (Utricle and Saccule): Detect linear movements (forward/backward) and gravitational forces.

    • Utricle: Detects movements in the horizontal plane.

    • Saccule: Detects movements in the vertical plane.

    • Within these organs, hair cells detect movement when otoconia (calcium carbonate crystals) shift in response to head position or linear acceleration.

• Why it Matters: It helps us maintain balance and posture, keeping the head upright in relation to movement.

• Reactivity Levels:

  • Hyperreactive: Individuals are highly sensitive and often insecure on moving surfaces, sometimes described as gravitationally insecure. In a playground setting, they might avoid climbing or equipment that involves dynamic movement.

  • Hyporeactive (Under-reactive): Individuals often lack safety awareness and may engage in risky movements without realizing potential danger.

• Clinical Example: Vertigo is a common symptom of vestibular dysfunction, where one feels a sensation of spinning or imbalance even when stationary, due to the inner ear not correctly registering stillnes.

• Class Activity: Turning $360$ degrees while nodding the head was demonstrated to highlight the internal sensations of vestibular input.

Emotions and Emotional Regulation

Infant Emotional Development

• Babies experience pain from birth.

• $6$ weeks: Start displaying social smiles and laughter. Begin to concentrate and focus on parents.

• $6$ months: Emotional expression intensifies. Babies can experience anger (e.g., hard crying) and sadness.

  • **Response to