Visual Cues: Depth, Form, and Motion

Visual Cues

• Visual cues allow perceptual organization, considering depth, form, motion, and constancy
• Inferences are made when looking at something
• Binocular cues use two eyes to perceive depth
  • Retinal disparity results from eyes being ~2.5 inches apart, providing slightly different views for depth perception
  • Convergence informs depth perception based on eyeball muscle strain
    • Relaxed eye muscles indicate distant objects
    • Contracted eye muscles indicate close objects
• Monocular cues require only one eye for visual stimuli received
  • Relative size: Closer objects appear larger, indicating form
  • Interposition (overlap): Overlapping objects are perceived as being in front
  • Relative height: Higher objects are perceived as farther away
  • Shading and contour: help with perceiving form, depth, and contours utilizing light and shadows
• Motion parallax ("relative motion"): Farther objects appears to move slowly, closer objects appear to move faster. Gives sense of motion
• Constancy: perceiving objects as the same even when the image cast on the retina changes
  • Size Constancy: Perceiving objects as the same size regardless of distance
  • Shape Constancy: Perceiving objects as the same shape even if the shape we see changes
    • Example: A door opening its shape is changing... still believe the door is a rectangle
  • Color Constancy: Perceiving objects as the same color despite changes in lighting

Sensory Adaptation

• Sensory adaptation adapts sensitivity to stimuli
• Hearing adaptation: Inner ear muscles contract in response to high noise, dampening vibrations and protecting the eardrum; ineffective for sudden loud noises
• Touch: Temperature receptors desensitize over time
• Smell: Receptors desensitize to molecule sensory information over time
• Proprioception: Sense of body position in space i.e. "sense of balance/where you are in space"
  • Experiment use goggles to make everything upside down for the perception of the world, and eventually will accommodate over time, and flip it back over
• Sight
  • Down regulation: Light adaptation causes pupils to constrict, desensitizing rods and cones during bright light exposure
  • Up regulation: Dark regulation causes pupils to dilate. rods and cones synthesizing light sensitive molecules

Weber's Law

• Just noticeable difference (JND) refers to the threshold for detecting a change in sensation
• Weber's Law : ΔI (JND) / I (initial intensity) = k (constant)
  • Example: 0.2/2 = 0.5/5 = 0.1, change must be 0.1 of initial intensity to be noticeable
• Weber’s Law predicts a linear relationship between incremental threshold and background intensity
• ΔI = Ik
• Plotting shows I against ΔI is constant

Absolute Threshold of Sensation

• Absolute threshold of sensation is the minimum stimulus intensity required for detection 50% of the time
• Detection can vary between individuals at low stimulus levels
• Absolute threshold is related to but distinct from the difference threshold (JND)
• Psychological states can influence the absolute threshold
  • Expectations (Are you expecting a text?)
  • Experience (How familiar are you with vibration sound)
  • Motivation (Are you interested in the text response)
  • Alertness (Are you awake our drowsy)
• Subliminal stimuli are below the absolute threshold

Somatosensation

• Somatosensation receives information regarding intensity, timing, and location of stimuli
• Includes sensing temperature (thermoception), pressure (mechanoception), pain (nociception), and position (proprioception)
• Intensity is determined by neuron firing rate
  • Slow firing implies low intensity
  • Fast firing implies high intensity
• Timing involves three patterns of neuron encoding
  • Non-adapting: Consistent firing rate
  • Slow-adapting: Slower firing rate to stimulus
  • Fast-adapting: Firing at stimulus onset, stopping, then restarting when stimulus changes
• Location specific stimuli relies on dermatomes and is sent to the brain by nerves

The Vestibular System

• The vestibular system controls balance and spatial orientation
• Input comes from both the inner ear and limbs
• Semicircular canals in the inner ear which are posterior, lateral and anterior detect head rotation
• Endolymph fluid shifts in the semicircular canals enabling the detection of head direction and rotation strength
• Otolithic organs (utricle and saccule) detect linear acceleration and head positioning
• CaCO3 crystals attached to hair cells in viscous gel trigger an action potential and move when transitioning between laying down and standing up.
• Dizziness and vertigo can occur when endolymph continues to move

Signal Detection Theory

• Signal detection theory studies decision-making under uncertain conditions, differentiating between important stimuli and noise
• Considered discerning between important stimuli and unimportant stimuli ("noise")
• Origins come from sonar- detecting small fish vs large whale
• Considers hits, misses, false alarms, and correct rejections
  • Hit: Affirmative response to a present signal
  • False Alarm: Signal perceived when absent
  • Correct Rejection: Correctly identifies the absence of a signal
  • Miss: Failure to respond to a present signal
• *Note: This is different terminology to Type I / Type II errors
• Signal Strength (d') is variable
  • hit > miss (when there is a strong signal)
  • miss > hit (weak signal)
• Strategy of signal detection (c)
  • Conservative strategy: Never affirm unless certain, leading to fewer false alarms and potential misses
  • Or Liberal strategy: Always affirm, leading to more true positives and potential false alarms