Sensation and Perception

• Sensation and perception are separate but related processes.
• Sensation involves detecting stimuli from the environment through sense organs and receptor cells.
• Perception is the process of organizing sensations into meaningful patterns, giving them order and meaning.
• Hearing sounds and seeing colors are sensory processes, while forming a melody and detecting patterns are perceptual processes.

Sensory Thresholds and Sensory Adaptation

• Sensory threshold and sensory adaptation explain how sensation works.
• Sensory threshold is the minimum point of intensity at which a sound can be detected.
• Absolute threshold (Limen) is the minimum level of stimulation that can be detected.
• Example: A cup of coffee needs a certain amount of sugar to taste sweet.
• Absolute threshold is also affected by physical and psychological factors like response-bias.
• Absolute threshold is defined as detecting a stimulus 50% of the time.
• Absolute Thresholds of the Senses in humans:
  • Vision: A candle flame viewed from about 30 miles on a clear, dark night.
  • Hearing: A watch ticking from about 20 feet away in a quiet room.
  • Taste: 1 teaspoon of sugar dissolved in 2 gallons of water.
  • Smell: About one drop of perfume diffused throughout a small house (1 part in 500 million).
  • Touch: The pressure of a fly's wing falling on a cheek from about 0.4 inch.
• Difference threshold (just noticeable difference - JND) is the minimum change in a stimulus needed to recognize a change.
• The difference threshold varies from person to person and occasion to occasion.
• Psychologists define difference threshold as the minimum change in stimulation detectable 50% of the time.
• Sensory adaptation is the decreasing responsiveness of sensory receptors to unchanging stimuli.
• Sensory adaptation helps detect important environmental changes by ignoring unchanging aspects.
• Example: People living in “Kera"/Addis Ababa stopped noticing the bad smell.
• Extremely intense sensations may not be subject to sensory adaption
• Adapting to harmful stimuli might be dangerous or fatal.

Perception

• Perception is the meaning-making process. The major characteristics include:
  • Selectivity of perception (attention)
  • Form perception
  • Depth perception
  • Perceptual constancy, and perceptual illusion.
• Selectivity of perception (Attention) refers to the perceptual process that selects certain inputs for inclusion in conscious experience, while ignoring others.
• The selectivity of perception implies that our field of experience is divided into Focus & - Margin.
• Events or stimuli perceived clearly are the focus, while dimly or vaguely perceived stimuli are in the margin.
• Attention shifts constantly.
• Paying attention depends on external (stimuli) and internal (perceiver) factors.
• External factors include size, intensity, repetition, novelty, and movement.
• Bigger, brighter, more frequent, newer, or moving stimuli are more likely to get your attention.
• Paying attention is not determined only by the characteristics of objects, but also on psychological factors.
• Two important psychological factors are "Set or expectancy" and "Motives or needs".

Form Perception

• Visual sensations provide raw materials to be organized into meaningful patterns, shapes, forms, and concepts.
• Meaningful shapes, patterns, or ideas made from discrete sensations make up form perception.
• Perceiving forms requires distinguishing a figure (object) from its ground (surroundings).
• Contours are formed whenever a marked difference occurs in brightness or color of the background, assisting to separate forms from the general ground.
• According to Gestalt psychology, when several objects are present in the visual field, the whole is more than the sum of its parts.
• Organization in perception partially explains our perception of complex patterns as unitary forms, or objects.

Laws of Perceptual Organization

• Law of Proximity: Items close in space or time are perceived as belonging together or forming an organized group.
• Law of Similarity: Similar items tend to be organized together.
• Law of Good Figure: Tendency to organize things to make a balanced or symmetrical figure.
• Law of Continuity: Tendency to perceive a line that starts in one way as continuing in the same way.
• Law of Closure: Perceptual processes organize the perceived world as complete by filling in gaps.
• Law of Common Fate: Tendency to group objects as part of the same group if they move together in the same direction.

Depth Perception

• Depth perception is our judgment of the world in three dimensions (distance or depth of objects).
• Depends on the use of binocular cues (require two eyes) and monocular cues (require one eye).
• Binocular cues:
  • Retinal disparity is the degree of difference between the image of an object focused on the two retinas. The closer the object, the great the disparity.
  • Convergence is the degree to which the eyes turn inward to focus on an object. The closer the objects the greater the convergence.
• Monocular cues help people with sight in only one eye to gauge depth
  • Accommodation is the change in the shape of the lens which allows focus on the retina. Accommodation can alter your depth perception.
  • Motion parallax is the tendency to perceive ourselves as passing objects faster when objects are closer than when they are farther away.
  • Pictorial cues: Cues artists utilize for their drawings and paintings, like interposition, relative size, linear perspective, elevation, shading patterns, aerial perspective, and texture gradient.
    • Interposition: Objects that overlap another object appear closer.
    • Relative size: If two equally tall people take up different amounts of space on your retina, the one who takes up less space is further away.
    • Linear Perspective: Objects that have parallel lines seem to get closer together as they get further away.
    • Elevation: The higher objects are in your visual field, the further away they are from you. This effect can be re-produced in painting to give depth
    • Shading patterns: Areas that are in shadow tend to recede, while areas that are in light tend to protrude.
    • Aerial Perspective: Closer objects appear clearer that more distant ones.
    • Texture Gradient: More details can be seen on the nearest objects, and fewer details can be made out ont he objects in the distance.

Perceptual Constancies

• The image of an object on the retina can vary in size, shape, and brightness, but we continue to perceive the object as stable due to perceptual constancy.
  • Size constancy is the interpretion of a change in retinal size as a change of distance
  • Shape constancy is the capacity to see maintain the actual shape of a known object from any angle.
  • Brightness constancy is the unchanging perception of an objects consistent brightness, regardless the amount of light reflected.

Perceptual Illusion

• Illusions are misperceptions or false perceptions of an object.
  • Visual or Optical illusions are physical stimuli that consistently produce errors in perception, like the Moon illusion and Muller-Lyer illusion.
  • Visual or auditory hallucinations are sensory experiences and perceptions that do not correspond to reality.
  • Delusions are unfounded beliefs that are strongly held despite a lack of evidence. The three common types are:
    • Delusion of persecution: You believe you are being persecuted by dangerous enemies
    • Delusion of grandeur: You are an important person, maybe a special messenger from God or similar.
    • Delusion of reference: The tendency to believe that others are giving you messages, either directly or through the television, radio, or internet.
• Extra Sensory Perception (ESP) or Paranormal Ability is perception that occurs independently of the known sensory processes:
  • Telepathy (thought transference) is the ability to read minds.
  • Clairvoyance is the ability to see events without being physically present.
  • Precognition is the ability to see into the future.
  • Mediumship is the ability to communicate with the spiritual world.
  • Clairgustance is the paranormal ability to taste a substance without putting it in the mouth.