Chapter summary imageHow do we experience and interpret the world around us?

WHAT ARE SENSORY THRESHOLDS?

  • An absolute threshold is the smallest amount of energy needed to detect a stimulus such as light, sound, or pressure 50% of the time.
  • A difference threshold is the minimum difference between two stimuli needed to detect the difference 50% of the time.

HOW DO WE PROCESS STIMULI FROM THE OUTSIDE WORLD?

  • Sensation occurs when a receptor cell in one of the sense organs is stimulated by energy. Transduction is the process of converting physical energy into electrochemical codes.
  • Light enters the eye through the cornea and pupil and is focused by the lens on the retina. Light waves are transmitted to the ganglion cells that make up the optic nerve. Neural messages travel along the optic nerve to the visual cortex.
  • Sound waves cause the eardrum to vibrate. Vibrations are carried to the cochlea, causing ripples in the basilar membrane. Hair cells in the basilar membrane stimulate receptor cells to send messages to the auditory cortex.
  • Airborne molecules stimulate receptor cells at the top of the nasal cavity, sending messages to the brain’s olfactory bulb.
  • Microvilli at the tips of receptor cells in the taste buds send messages to the limbic system and cerebral cortex. The five basic taste qualities are sweet, sour, salty, bitter, and umami.
  • Receptor cells in skin process pain, pressure, and temperature. Pain is currently explained by the gate-control theory.
  • The kinesthetic senses provide information about muscle movement and changes in posture. The vestibular senses provide information about the body’s position in space.

WHY ARE WE ABLE TO EXPERIENCE ONLY ONE PERCEPTION AT A TIME?

  • Perception is the brain’s process of organizing and making sense of sensory information.
  • Conscious attention is selective—we can only experience one perception at a time. Failure to perceive a stimulus is known as inattentional blindness.

WHAT ARE SOME MAJOR THEORIES OF PERCEPTION?

  • Gestalt psychologists point out that we group stimuli together when the objects are near each other; are similar sizes, colours, and shapes; or complete a pattern.
  • Treisman’s feature integration theory proposes that we use parallel processing to detect visual features, then serial processing to combine them.

IS PERCEPTION DEVELOPED BY NATURE OR NURTURE?

  • Normal sensory and perceptual development takes place during a critical period shortly after we are born.
  • Perceptual adaptation enables us to adjust to changes in the way we perceive the environment.
  • People who interpret sense information as more than one sensation have a condition called synaesthesia, in which signals from the sensory organs are processed in the wrong cortical areas of the brain.