Sensation - Senses and Perception PDF

**SENSATION** - **Definition**: The process of detecting information from the external world through the sense organs. - **Stimulus**: Any form of energy or event that activates a sense organ (e.g., light, sound, chemicals, touch). - **Characteristics of Sensation**: 1. **Abso...

**SENSATION** - **Definition**: The process of detecting information from the external world through the sense organs. - **Stimulus**: Any form of energy or event that activates a sense organ (e.g., light, sound, chemicals, touch). - **Characteristics of Sensation**: 1. **Absolute threshold**: The minimum amount of energy required to activate a sense organ. Stimuli below this level are not detected. 2. **Differential threshold**: The smallest difference in stimulation required to detect a change in stimulus intensity. 3. **Sensory adaptation**: A decrease in sensitivity to a constant stimulus over time, leading to a reduced ability to sense that stimulus. **THE SENSORY SYSTEMS** **A. Visual Sense (Sight)** - **Definition**: The ability to detect light and interpret visual stimuli using the eyes. - **Stimulus**: Light, which is a form of electromagnetic energy, with wavelengths between 400-700 nm visible to humans. - **Parts of the Eye**: - **Cornea**: Transparent outer membrane of the eye that helps focus light. - **Aqueous humor**: Fluid between the cornea and the lens. - **Pupil**: The opening in the iris that regulates the amount of light entering the eye. - **Iris**: The colored part of the eye; controls pupil size. - **Lens**: Focuses light onto the retina by changing its shape. - **Retina**: The light-sensitive layer at the back of the eye that contains photoreceptors (rods and cones). - **Rods**: Photoreceptors responsible for night vision and black-and-white vision. - **Cones**: Photoreceptors responsible for color vision and daylight vision. - **Fovea**: The center of the retina where vision is sharpest. - **Blind spot**: The area where the optic nerve leaves the eye; no photoreceptors present. **B. Auditory Sense (Hearing)** - **Definition**: The ability to detect sound waves through the ear and interpret auditory information. - **Stimulus**: Sound waves, which are changes in atmospheric pressure causing air molecules to vibrate. - **Parts of the Ear**: - **Outer ear**: Consists of the pinna (external part), auditory canal, and eardrum (tympanic membrane). - **Middle ear**: Contains three ossicles (hammer, anvil, stirrup) that amplify sound vibrations. - **Inner ear**: Includes the cochlea (fluid-filled structure responsible for converting sound waves into nerve impulses) and the organ of corti (contains hair cells that detect sound). **C. Olfactory Sense (Smell)** - **Definition**: The sense that detects airborne chemicals (odors) through receptors in the nasal passages. - **Stimulus**: Airborne chemicals that bind to receptors in the olfactory epithelium. - **Olfactory epithelium**: A layer of tissue in the nasal cavity that contains smell receptors. - **Basic odors**: Fragrant, fruity, spicy, putrid, resinous, and burned. - **Anosmia**: A condition characterized by the inability to perceive smells, often caused by drug reactions or illness. **D. Gustatory Sense (Taste)** - **Definition**: The sense responsible for detecting dissolved substances (taste) through receptors on the tongue. - **Stimulus**: Substances dissolved in saliva that stimulate taste buds. - **Taste buds**: Sensory receptors located in the papillae of the tongue. - **Four primary tastes**: Sweet, sour, bitter, salty. **E. Somesthetic Sense (Skin Senses)** - **Definition**: The sensory system responsible for detecting touch, temperature, and pain through receptors in the skin. - **Receptors**: Sensory cells located in different layers of the skin. - **Touch**: Detects pressure and vibration. - **Temperature**: Detects warmth and cold. - **Pain**: Alerts the body to potential harm or injury. - **Gate-control theory**: Explains how the brain can regulate pain perception by opening or closing neural \"gates.\" **F. Kinesthetic Sense** - **Definition**: The sense responsible for detecting body movement, posture, and orientation through receptors in muscles, joints, and tendons. **G. Vestibular Sense** - **Definition**: The sensory system that detects balance, body position, and motion. - **Receptors**: Located in the semicircular canals and vestibular sacs of the inner ear; responsible for detecting changes in body position and motion (e.g., tilting, moving). **PERCEPTION** - **Definition**: The brain's process of interpreting sensory information to give it meaning. - **Subliminal Perception**: Perception of a stimulus below the conscious awareness threshold. **Factors Influencing Perception:** 1. **Stimulus conditions**: Size, intensity, movement, repetition, contrast of a stimulus. 2. **Personal factors**: Motivation, values, interest. **Principles of Perceptual Organization (Gestalt Psychology):** 1. **Proximity**: Objects close to each other are perceived as a unit. 2. **Similarity**: Similar objects are grouped together. 3. **Good continuation**: We tend to perceive smooth, continuous lines. 4. **Closure**: We mentally fill in gaps to perceive a complete figure. **Perception of Distance:** - **Binocular cues**: Use both eyes to perceive depth and distance (e.g., retinal disparity, convergence). - **Monocular cues**: Use one eye to perceive depth (e.g., linear perspective, relative size, overlap, texture gradient, atmospheric perspective). **Perception of Movement:** - **Real motion**: Actual movement of an object. - **Apparent motion**: 1. **Stroboscopic movement**: Seen in movies through rapid successions of still images. 2. **Autokinetic effect**: A stationary light appears to move in darkness. 3. **Induced movement**: Stationary object appears to move when the background moves. **Visual Illusions:** - **Definition**: Misinterpretations of visual stimuli, leading to false perceptions. - **Examples**: Muller-Lyer illusion, Poggendorf illusion. **Extra-Sensory Perception (ESP):** - **Definition**: Perception without the use of normal sensory processes. 1. **Telepathy**: Transfer of thoughts between individuals. 2. **Precognition**: Perceiving events before they occur. 3. **Clairvoyance**: Gaining information about distant objects or events. 4. **Psychokinesis**: Moving objects without physical contact. 5. **Astral projection**: An out-of-body experience in which a person's consciousness separates from the body and travels.