Sensation and Perception: Foundations of Psychological Experience

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Sensation and Perception

Introduction

Sensation and perception are foundational concepts in psychology, describing how we detect and interpret information from the environment. Sensation refers to the detection of physical energy by sensory organs, while perception involves the brain's interpretation of these sensory signals.

Transduction: Conversion of Energy

Transduction is the process by which sensory organs convert external stimuli into neural impulses.
Sensory receptor cells receive information and transform it into electrical signals (action potentials).
These signals are then delivered to the brain for interpretation.

The Multisensory Brain

Perception is based on building simple input into more complex perceptions.
Bottom-up processing: Perception begins with sensory input.
Top-down processing: Perceptual processes in which memory and other cognitive processes are required for interpreting incoming sensory information.

Sensory Adaptation

Activation is highest at first detection, then sensory adaptation occurs.
Sensory receptor cells become less responsive to unchanging stimuli, making them less noticeable over time.
This adaptation allows us to focus on novelty and changes in our environment.

Psychophysics: Measurement of Sensation

Absolute threshold: The minimum intensity of a stimulus that a person can detect half the time.
Example: Detecting a candle flame 48 km away on a clear night, or 1 tsp of sugar in 7.5 L of water.
Difference threshold (Just Noticeable Difference, JND): The smallest difference in stimulation that can be reliably detected.
Weber's Law: The JND between two stimuli is not absolute, but an amount relative to the magnitude of the stimuli.

Where k is a constant and I is the intensity of the stimulus.

Subliminal Perception

Perception of stimuli that are presented below the absolute threshold.
Practical application is limited (e.g., self-help tapes).

Attention in Sensation and Perception

The Role of Attention

Flexible attention is crucial for effective perception.
Selective attention: Focusing on a specific aspect of sensory input while ignoring other stimuli.
Attention acts as a bottleneck; unattended stimuli are still processed at some level.

Inattentional Blindness

Failure to detect an unexpected stimulus in plain sight due to limited attentional resources.
Example: Not noticing a person in a gorilla suit walking through a basketball game.

Change Blindness

Failure to detect changes in the environment.
Limited resources are further constrained by age, distraction, or other factors.

Examples of Inattentional and Change Blindness

Simulated studies show that people often miss significant changes in their environment, even when they are obvious.
Example: Police officers missing a fight staged during broad daylight.

Sensory Systems

Overview of the Senses

Vision (sight)
Audition (hearing)
Gustation (taste)
Olfaction (smell)
Touch (tactile)
Balance (vestibular)
Body awareness (proprioception)

Vision

Light-sensitive cells in the retina (rods and cones) detect light and color.
Retina: Inner surface of the eye containing photoreceptors.
Optic nerve: Carries neural impulses from the eye to the brain.
Blind spot: Point where the optic nerve leaves the eye; no receptor cells present.

The Eye: Vision's Window

The iris controls the amount of light entering the eye.
Pupil size adjusts to regulate light intake and can change with emotional arousal.

Rods and Cones

Rods: Detect black, white, and gray; sensitive to movement; function well in low light; located in the periphery.
Cones: Detect color and fine detail; function best in daylight; clustered around the fovea.

Colour Vision Theories

Trichromatic theory: Three types of cones (red, green, blue) respond to different wavelengths.
Opponent process theory: Colors are perceived in terms of opposing pairs (red-green, blue-yellow, black-white).

Colour Constancy

The ability to perceive an object as having a constant color under varying illumination conditions.
Example: A green apple appears green in both sunlight and shade.

Depth and Distance Perception

Monocular cues: Require only one eye (e.g., relative size, texture gradient, overlap, linear perspective).
Binocular cues: Require both eyes (e.g., retinal disparity, convergence).

Hearing (Audition)

Sensing Sound

Outer ear: Funnels sound toward the eardrum.
Middle ear: Contains three tiny bones (ossicles) that amplify vibrations.
Inner ear: Contains the cochlea, which transduces vibrations into neural signals.
Basilar membrane: Runs through the cochlea and vibrates in response to sound, stimulating hair cells.

Hearing Loss

Conductive deafness: Malfunctioning of the ear, especially the eardrum or ossicles.
Nerve deafness: Damage to the auditory nerve or hair cells.
Sudden sensorineural hearing loss: Rapid loss of hearing due to nerve damage.

Perceptual Organization

How We Organize Sensory Information

Perception is constructive; we interpret sensory input to create meaningful representations.
We use context, memory, and expectations to make sense of what we see.
Objects are perceived as constant and unchanging even when sensory input about them changes (size, shape, color).

Visual Agnosia and Blind Sight

Visual agnosia: Inability to recognize objects due to damage to higher visual cortical areas.
Blind sight: Ability to respond to visual stimuli without conscious perception, often due to damage to area V1.

Context and Emotion in Perception

Context Effects

Expectations, context, and prior knowledge shape perception.
Example: Perceiving a driver differently when you are a pedestrian versus when you are driving.

Emotional Influences

Sad music can lead to perceiving sad meanings in ambiguous stimuli.
Anger increases the likelihood that neutral stimuli will be interpreted as threatening.
Anxiety can cause physical sensations to be misinterpreted as panic.