APSY101 Chapter 4 (Part One)

CHAPTER 4: SENSATION AND PERCEPTION

• APSY 101: Introduction to Psychology

• Prof. Ocasio

• Spring 2025

Key Concepts of Sensation and Perception

Sensation

• The stimulation of sense organs through sensory input.

• Involves direct interaction with the environment through receptors.

Transduction

• The process where sensory stimuli are converted by receptor cells into electrical impulses.

• These impulses are then transported to the brain for interpretation.

Perception

• The organization and interpretation of sensory input by the brain.

• This allows us to understand and react to the stimuli around us.

Learning Objectives

1. Review the capacities and limitations of human sensation.

2. Understand the difference between sensation and perception.

3. Describe how psychologists measure sensory thresholds and difference thresholds.

Measuring Sensation

Psychophysics

• A branch of psychology examining how physical stimuli influence sensory perceptions.

Thresholds

• Absolute Threshold: The minimum intensity of a stimulus that can just barely be detected.

• Signal Detection Analysis: A method to assess a perceiver’s ability to distinguish true signals from noise.

  • Types of responses: present or absent stimulus; perceived as yes/no.

  • Measures:

    • Sensitivity: Actual ability to detect signals.

    • Response Bias: Tendency to respond positively ('yes').

Outcomes in Signal Detection

• Correct Rejections and Hits indicate accurate responses.

• Misses and False Alarms indicate errors in detection.

Difference Threshold (Just Noticeable Difference - JND)

• The minimum change in stimulus intensity that can be detected.

• Defined by Weber’s Law: JND is a constant proportion of the original stimulus intensity.

Key Takeaways on Sensation and Perception

• Sensation involves receiving environmental information via sensory organs.

• Perception is about interpreting this sensory input for understanding and reaction.

• Transduction converts environmental stimuli into signals for brain processing.

• Human sensory experiences are rich but have inherent strengths and limitations.

Signal Detection Influences

• Detection tasks influenced by the absolute threshold and individual motivations.

• Signal detection analysis differentiates between sensitivity and bias.

Vision

Electromagnetic Spectrum and Vision

• Vision detects electromagnetic radiation; visible light is a small part of the spectrum.

• Wavelength: Distance between wave peaks; shorter wavelengths appear blue, longer appear red.

Structures of the Eye

• Cornea: Clear covering that bends light.

• Pupil: Opening allowing light entry, controlled by the iris.

• Lens: Focuses light on the retina.

• Retina: Contains photoreceptor cells (rods and cones).

Photoreceptor Cells

• Rods: Sensitive to light; detect shades of gray.

• Cones: Sensitive to colors; fine detail perception.

• Fovea: Area with high concentration of cones for detailed vision.

Visual Processing

• Light enters through the cornea, passes through the pupil, and is focused by the lens onto the retina.

• Optic Nerve: Transmits information from the retina to the visual cortex.

• Blind Spot: Area in the retina lacking photoreceptors where optic nerve exits.

Depth Perception

Mechanisms of Depth Perception

• The ability to perceive three-dimensional space and distance.

• Visual Cliff: Used to assess depth perception in infants.

Depth Cues

• Oculomotor Convergence: Eyes turning inward to focus on nearby objects.

• Binocular Retinal Disparity: Differences in images from each eye.

• Monocular Depth Cues: Provide distance information from one eye.

  • Examples include relative height, relative size, linear perspective, etc.

Key Takeaways in Vision

• Vision processes electromagnetic energy and detects shape, color, motion, and depth.

• Light's path: enters through cornea ➡ pupil ➡ focused by lens ➡ retina (inverted image).

• The retina contains rods (detect black/white) and cones (detect color).

• Depth perception utilizes various cues for accurate spatial judgement.