Untitled Quiz

Sensation & Perception

• Sensation: Stimulation of the sense organs
• Perception: The selection, organization, and interpretation of sensory input.

Psychophysics

• Psychophysics: The study of how physical stimuli are translated into psychological experiences.
• Gustav Fechner (1860): Wrote "Elemente der Psychophysik."

Detection

• Stimulus: Any detectable input from the environment.
• Absolute Threshold: The minimum amount of stimulation that an organism can detect for a specific type of sensory input.
  • Arbitrarily defined as the stimulus intensity detected 50% of the time.

Just Noticeable Difference

• Just Noticeable Difference (JND): The smallest difference in the amount of stimulation that a specific sense can detect.
  • Also known as Difference Threshold
• Weber's Law: States that the size of a JND is a constant (Weber fraction) that is proportional to the size of the initial stimulus.
  • These constants differ depending on the type of sensory input!

Scaling

• We are used to measuring things on absolute scales (e.g., distances in meters).
• In perception, everything is relative; you can't use absolute scales!

Fechner's Law

• Fechner's Law: States that subjective sensation is proportional to the logarithm of the stimulus intensity.
  • As stimulus intensity increases, smaller and smaller increases are perceived in the magnitude of that sensation!

Signal Detection Theory

• Signal Detection Theory: Proposes that detection of stimuli involves decision processes as well as sensory processes.
  • Both processes are influenced by various factors besides stimulus intensity.

Perception & Awareness

• Subliminal Perception: The registration of sensory input without conscious awareness.
  • James Vicary (1957) controversially claimed subliminal messages ("Eat popcorn") increased popcorn sales in a theater.

Sensory Adaptation

• Sensory Adaptation: A gradual decline in sensitivity due to prolonged stimulation.
  • An adaptive process that makes us aware of changes in the environment rather than constants.

The Auditory System

• Sense of Hearing:

Sound as a Stimulus

• Sound waves are vibrations of molecules that travel through a medium, such as air.
  • These vibrations travel at a fraction of the speed of light.

Sound Waves

• Characterized by their amplitude, frequency, wavelength, and purity.

Frequency

• Measured in cycles per second or hertz (Hz).
• Pitch depends on frequency.

Wavelength

• Measured as a distance (e.g., nm, mm, cm, m).
• Pitch depends on wavelength.

Amplitude

• Measured in decibels (dB).
• Loudness depends mainly on amplitude.

Purity

• Viewed as a sound envelope.
• Timbre depends mainly on purity.

Hearing Capacities

• Lower Frequency (Hz):
  • Humans: 20
  • Dogs: 50
  • Cats: 45
  • Bats: 20
  • Dolphins: 0.25
  • Elephants: 5
• Upper Frequency (Hz):
  • Humans: 20,000
  • Dogs: 45,000
  • Cats: 85,000
  • Bats: 120,000
  • Dolphins: 200,000
  • Elephants: 10,000

The Human Ear

• Three major parts:
  • Outer (or external) ear
  • Middle ear
  • Inner ear

Theories of Hearing

• We focus on pitch perception.
  • Perception of loudness and timbre is not well understood.

Perception of Taste

• Perception of taste quality depends on complex patterns of neural activity initiated by taste receptors.
• Basic taste preferences may be innate and automatically regulated by physiological mechanisms.
  • However, most taste preferences are learned.

Perception of Taste

• Not everyone has the same ability to taste:
  • Non-tasters: Have a low taste sensitivity.
  • Supertasters: Have a high sensitivity to taste.
  • Medium tasters: Have an average taste sensitivity.
  • Variations in sensitivity lead to different sensory experiences when tasting the same food.

Perception of Taste

• Taste sensitivity influences eating habits.
  • Supertasters tend to have better health habits than non-tasters.
  • Women are more likely to be supertasters than men.

Perception of Flavour

• Flavour is a combination of taste, smell, and the tactile sensation of food in one's mouth.
  • Odours are crucial to the perception of flavour.

The Olfactory System

• Sense of Smell:
  • Humans are relatively insensitive to smell.

The Olfactory System

• Stimuli are volatile chemical substances that easily evaporate at room temperature.
• Receptors are olfactory cilia, hair-like structures located in the upper portion of the nasal passages.

The Olfactory System

• Buck & Axel (1991) clarified the mechanisms involved in odour recognition.
  • Identified a gene set consisting of 1000 different genes affecting the operation of olfactory receptor cells.
  • Won the Nobel Prize in 2004 for their work!

Seeing

• Wavelength: Determines hue (colour).
• Amplitude: Determines brightness (value).
• Purity: Determines saturation.

Colour Mixture

• Additive Colour Mixing: Superimposes lights, adding light to the mixture.
• Subtractive Colour Mixing: Removes wavelengths of light, reducing the amount of light present.

Trichromatic Theory

• The human eye has three types of receptors (cones) with differing sensitivities to different light wavelengths.
  • Each cone is sensitive to specific wavelengths of red, green, or blue.
  • All colours are created by an additive mixing process.

Trichromatic Theory

• Explains colour blindness.
  • Most colour-blind individuals are dichromats, lacking sensitivity to either red, green, or blue.

Colour Blindness

• A red/green colour-blind person will confuse blue and purple because they can't perceive the red element of purple.

Opponent-Process Theory

• The human eye has three types of receptors (cones), each sensitive to two wavelengths.
  • Red or Green
  • Blue or Yellow
  • Black or White

Opponent-Process Theory

• Explains afterimages, the visual image that persists after a stimulus is removed.

Dual-Process Theory

• Combines trichromatic and opponent-process theories, taking into account the three types of cones and their sensitivity to different wavelengths.

Depth Perception

• Depth Perception: Interpretation of visual cues that indicate the nearness or distance of objects.
  • Cues can be monocular or binocular.

Depth Perception

• Monocular Depth Cues: Rely on the image in either eye alone:
  • Motion Parallax: Relative motion of objects across the retina.
  • Pictorial Depth Cues: Linear perspective, texture gradients, interposition, relative size, height in plane, light and shadow.

Depth Perception

• Binocular Depth Cues: Rely on the differing views from both eyes:
  • Retinal Disparity: Objects project images to slightly different locations on the left and right retinas; the eyes see slightly different views.
  • Convergence: The feeling of the eyes converging toward each other as they focus on closer objects.

Cognition and Vision

• Bottom-up Processing: Emphasizes the stimulus characteristics important in recognizing an object.
  • Starts with individual elements, puts them together, and interprets the object as a whole.

Top-down Processing

• Interprets sensory information based on existing knowledge, concepts, and ideas.
  • Contextual factors and expectations can affect the speed of object recognition.
  • Strong when stimuli are incomplete or ambiguous.

Gestalt Psychology

• Humans have basic tendencies to actively organize what they see.
  • The whole is greater than the sum of its parts (top-down processing).
  • Gestalt: Has an overall quality that transcends the individual elements.

Gestalt Psychology

• Figure-ground relationship: Organizing scenes into a central figure (focus) and a background.
  • Humans are good at focusing on figures!
• Ambiguous figure-ground relationships: Allow for multiple interpretations.

Gestalt Reversals

• Bottom-up: The neurons in the visual cortex become adapted to one figure, making it more likely to see the alternative.
• Top-down: People actively try to solve the visual paradoxes by switching between two reasonable solutions.

Illusory Contours

• You can 'see' boundaries that don't exist!

Gestalt Laws of Organization

• 1. Law of Similarity: Similar objects are seen as belonging together.
• 2. Law of Proximity: Objects near each other are seen as belonging together.
• 3. Law of Closure: People tend to perceive incomplete figures as complete.