Psych 100: Perception and Depth Cues

Introduction to Perception

• Focus of lecture: Depth cues and how we perceive distance.

• Importance of depth perception:

  • Critical skill for survival.

  • Essential for judging whether objects can be reached or avoided.

Depth Perception

• Combination of genetic factors and learning.

• Early experiments to study inborn depth perception:

  • Visual Cliff apparatus:

    • Design: Table with a grid pattern; one side appears to have a drop-off covered by glass.

    • Experiment: Baby placed on the edge and called to crawl.

    • Findings: By six months, children avoid crawling over the edge, indicating some innate perception of risk.

  • Learning about depth starts immediately:

    • Example: A newborn's visual experience in the hospital (reaching towards mother).

    • Research indicates even days after birth, infants respond to looming shapes.

Cues for Depth Perception

• Types of cues:

  • Binocular Cues: Need both eyes.

  • Convergence:

    • Definition: The inward angle of the eyes when focusing on an object.

    • Utility: Effective for distances up to 50 feet; provides feedback via eye muscles.

  • Accommodation:

    • Definition: Change in shape of the eye's lens based on distance from the object.

    • Importance: Essential for infants; helps in distinguishing reachable objects.

    • Effective for about four feet.

  • Retinal Disparity:

    • Definition: The slight difference in images received by each eye.

    • Function: Used to perceive depth; greater differences indicate closer proximity.

    • Application in 3D films: Uses separate images for each eye to create depth perception.

• Pictorial Cues: Exist within the image itself.

  • Linear Perspective:

    • Concept: Parallel lines appear to converge in the distance, creates depth.

  • Relative Size:

    • Concept: Objects that appear smaller are perceived as farther away.

  • Height in the Picture Plane:

    • Concept: Higher objects in a visual field appear farther away.

  • Light and Shadow:

    • Function: Shadows provide cues for depth and shape.

    • Example: Apollo 12 mission—astronauts misjudged distances based on shadow appearance.

  • Overlap (Interposition):

    • Concept: Objects that occlude others are perceived as being closer.

  • Texture Gradients:

    • Concept: Detail in surface textures decreases with distance.

  • Aerial Perspective:

    • Definition: Clarity of objects diminishes with distance due to atmospheric particles.

    • Example: Distant landscapes appear hazier on smoggy days.

  • Relative Motion (Motion Parallax):

    • Concept: Moving closer objects appear to speed past while distant objects appear to move more slowly.

Optical Illusions of Depth

• Moon Illusion:

  • Observation: Moon appears larger on the horizon than overhead despite actual size remaining constant.

  • Factors for perception:

  • Retinal image size remains the same; perceived distance differs.

  • Emmert's principles:

    • Retinal image size, perceived distance, perceived size determination.

    • Supportive cues at the horizon (hills) mislead us into perceiving greater distance.

• Ponzo Illusion:

  • Observation: Two horizontal lines appear different in length due to converging lines suggesting depth.

• Müller-Lyer Illusion:

  • Observation: Two lines of identical length, one with outward and the other with inward-facing arrowheads, perceived differently.

  • Reasons: Perceived depth cues simulate three-dimensionality, affecting depth comprehension.

Perceptual Learning and Habits

• Perceptual Learning: Changes in perception occurring through experience, leading to alterations in brain processing.

  • Example: Expertise in identifying different species (rodents, trees, etc.) alters perception.

• Perceptual Habits: Patterns in attentional focus that lead to differences in perception among individuals.

  • Example: Differences in noticing clothing details or car types related to personal interests.

Processing Movement in Vision

• Smooth Pursuit:

  • Definition: Eyes moving in a smooth manner while following an object.

  • Function: Useful in processing visual information continuously.

• Saccades:

  • Definition: Rapid eye movements from one focal point to another.

  • Function: Information is processed only before and after the movement, not during.

Attention and Perception

• Attention significantly influences perception.

  • Factors affecting attention-getting stimuli:

  • Intensity: More intense stimuli are easier to notice.

  • Repetitive Nature: Repeated stimuli become more noticeable over time.

  • Speed of Change: Abrupt changes are easier to perceive than gradual ones.

  • Contrast: Greater contrast in quieter settings captures attention better.

Adaptation at Sensory and Cognitive Levels

• Habituation: Process of reducing response to repetitive stimuli, e.g., snails retracting feelers after constant touch.

• Example: Residents near train tracks: initial loudness fades as they adapt.

Motivation's Influence on Perception

• Current emotional state affects perception significantly.

  • Scary movie example: perceptions of ordinary sounds change based on prior viewing experiences.

  • Emotional states can distort interpersonal perceptions, leading to misinterpretations.

Bottom-Up and Top-Down Processing

• Bottom-Up Processing: Assembly of perception from fragments without pre-existing knowledge.

• Top-Down Processing: Application of existing knowledge or expectations to interpret elements within perception.

Perceptual Sets and Expectancies

• Perceptual Sets: Expected characteristics based on context or categorization influences perception.

  • Example: Memory recall of a video varies with suggestive labels about the protagonist’s occupation (waitress vs. librarian).

Eyewitness Testimony and Errors

• Importance of accurate eyewitness testimony in criminal cases.

  • Variability in accuracy depending on individual aptitude for detail, emotional response, and circumstances.

• Study by Elizabeth Loftus shows:

  • Staged assault's details recalled accurately only about 25% of the time, indicating significant error potential.

  • Importance of eyewitness familiarity: biases based on personal interests impact detail perception.

  • Emotional intensity in situations (e.g., presence of weapons) diminishes accuracy of witnesses.

  • Post-event questions can distort memories.

Conclusion

• Understanding perception is vital for both psychological science and practical applications in everyday life.

• Future lectures will explore related topics like learning as we move forward.