Lecture 4: Sensation & Perception I – Principles and Vision

Principles of Sensation & Perception

Introduction

Sensation and perception are foundational topics in psychology, focusing on how organisms detect and interpret information from the environment. Sensation refers to the process of sensing our environment through touch, taste, sight, sound, and smell, while perception is the way we interpret these sensations and make sense of everything around us.

Sensation vs. Perception

• Sensation: The biological process of detecting physical stimuli from the external world and converting it into neural signals.

• Perception: The cognitive process of organizing and interpreting sensory information to produce meaningful experiences and guide behavior.

• Dissociation: Sensation and perception can be dissociated in certain neurological conditions (e.g., prosopagnosia, where face perception is impaired despite intact sensation).

• Neural Pathway: Sensory receptors → thalamus → cortex.

Example: The famous 'dress' illusion demonstrates how perception can differ even when the sensory input is the same, highlighting the ambiguity and interpretive nature of perception.

Psychophysics & Thresholds

Introduction

Psychophysics is the study of the relationship between physical stimulus properties and the sensations and perceptions they produce. It helps us understand how we detect and differentiate stimuli.

Types of Thresholds

• Absolute Threshold: The minimum intensity of a stimulus that can be detected 50% of the time.

• Difference Threshold (Just Noticeable Difference, JND): The smallest difference in stimulus intensity that can be detected 50% of the time.

• Weber's Law: The difference threshold is proportional to the initial stimulus intensity. Mathematically, $\Delta I / I = k$ where $\Delta I$ is the change in intensity, $I$ is the initial intensity, and $k$ is a constant.

Examples of Absolute Thresholds

Sense	Threshold Example
Vision	A candle flame 30 miles away on a dark, clear night
Hearing	A watch ticking 20 feet away
Smell	A drop of perfume in a six-room house
Taste	A teaspoon of sugar in a gallon of water
Touch	The wing of a fly falling on your cheek from 1 cm

Signal Detection Theory

• Addresses how decision-making occurs in the presence of uncertainty.

• Considers both the intensity of the stimulus and psychological factors (e.g., expectations, motivation).

Vision (Preview)

Introduction

Vision is one of the most studied senses in psychology, involving complex processes from the detection of light to the interpretation of visual scenes. The next section will cover the anatomy of the eye, visual pathways, and theories of color vision.

Key Concepts (to be expanded in full vision section)

• Transduction: Conversion of light into neural signals by photoreceptors in the retina.

• Visual Pathways: Information travels from the retina → optic nerve → thalamus → visual cortex.

• Feature Detection: Specialized cells respond to specific aspects of visual stimuli (e.g., edges, movement).

Additional info:

• Perceptual illusions (such as ambiguous figures and color illusions) demonstrate the interpretive nature of perception and the brain's role in constructing reality.

• Prosopagnosia is a neurological disorder characterized by the inability to recognize faces, illustrating the separation between sensation and perception.