Notes on Vision, Perception, and Cognition (Sensation vs Perception; grouping, depth cues, context)

Overview

• The course is organized around three pillars explaining psychological phenomena: contributions of the body (neuroscience/physiology), the mind (cognition/learning/memory), and the environment. The current quarter focuses on neuroscience and perception (the body’s contribution to vision and other senses).
• Two goals for today:
  • Small goal: finish up vision and examine the role of cognition in how we see the world (learning, memory, expectation, experience) and how thinking shapes perception.
  • Large goal: begin the shift from physiology to cognition in general, laying groundwork for understanding thinking, knowledge acquisition, memory storage/retrieval, decision making, problem solving, biases, and intelligence.
• Big transition: move from the first pillar (neuroscience) into the second pillar (cognition) and preview the tools and approaches for understanding psychological experience and behavior.
• Preview of future topics: after the exam, explore cognition broadly—what it means to think, how we learn, how memory works, how we apply knowledge, biases, and differences in intelligence, plus how those ideas will be tested.

Sensation and Perception: core concepts

• Sensation vs Perception (two related but distinct processes):
  • Sensation: the physiological processes of recording stimuli and the retinal image (the data collection stage).
  • Perception: the mental processes of interpreting and understanding the sensory input from the world.
• Textbook framing: the unit is titled sensation and perception to signal the integration of physiology (sensation) and cognition (perception).
• Practical takeaway: perception is not a direct readout of the world; it is shaped by cognition, expectations, experience, and context.

Vision: from physiology to cognition

• Physiological view recap: the eye and visual pathways encode specific features; perception arises when specific neurons fire in response to those features.
  • Example: color vision
  • Neurons fire in a particular pattern when seeing red; that neural activity creates the experience of red.
  • Different neurons fire for green, etc.
  • Other visual features: edges, lines, curves, squares, motion, faces, etc.
• Limitation of physiology alone: even with a physiological account, perception also depends on cognition—expectations and context can alter what we see (e.g., recognizing a roommate’s face).
• Cognitive contributions: learning, memory, expectation, and prior experience influence perception; perception is not a purely bottom-up process.
• Key terms introduced for the course: sensation (physiology) vs perception (cognition).

Perceptual organization: grouping, depth, and interpretation

• The mind does not passively record, it actively interprets features recorded by the eyes.
• Four examples of how cognition shapes perception (grouping and interpretation):
  • Grouping rules (gestalt-inspired ideas): how features are organized into meaningful units.
  • Depth perception: how we infer 3D structure from 2D retinal input.
  • Perceptual set: a bias to interpret ambiguous stimuli in a particular way.
  • Context and background: who we are (and our cultural background) influences perception.
• The Necker Cube and subjective contours illustrate how perception can change with interpretation and with contingent cues.

Ambiguity and grouping: four grouping rules (subconscious mental rules)

• Ambiguous image example: old woman vs. young woman; same retinal data, different perceptual interpretation.
• Four grouping rules (mental shortcuts the brain tends to use):
  • Proximity: elements close to each other tend to be grouped together.
  • Similarity: elements that look alike (shape, color) tend to be grouped.
  • Continuity: we tend to see continuous lines and patterns rather than abrupt changes; we impose a single coherent form.
  • Connectedness (and other features): items that are connected or linked in some way tend to be perceived as a unit (e.g., eyeglasses linking two eyes).
• Examples to illustrate rules:
  • Proximity: eight vertical lines appear as four pairs due to closeness.
  • Similarity: a column pattern of triangles and circles is perceived based on shape and color similarity.
  • Continuity: a line arrangement is perceived as a continuous path rather than disjoint segments; the brain fills in missing edges (subjective contours).
  • Connectedness: eyeglasses or other linking features can group two otherwise separate elements.

Subjective contours and the Necker cube as demonstrations of top-down processing

• Necker Cube illusion: an ambiguous line figure that can be perceived as a cube in different orientations.
• Subjective contours: edges that seem to exist due to perceptual inference (the mind fills in edges that aren’t physically drawn).
• “Cue behind the wall” demonstration:
  • When the cube is imagined as behind a wall, the subjective contours disappear because the brain infers there is no need to fill in edges.
• Lesson: perception relies on rules like continuity and context, and changing interpretation changes the perceived figure without changing the retinal image.

Depth perception: turning 2D input into 3D understanding

• The depth paradox: retinal images are 2D, yet we experience a 3D world.
• Mental rules (depth cues) help bridge the gap from 2D to 3D.
• Binocular cues (stereopsis): differences between the two eyes’ views provide depth information when two slightly different retinal images are fused.
  • The brain compares the two retinal images to infer depth (distance of objects).
  • Binocular cues require two eyes, but depth can be perceived with one eye via monocular cues.
• Monocular cues to depth (static and moving):
  • Relative size: smaller objects are perceived as farther away if the objects are known to be similar in size.
  • Interposition (occlusion): if one object partially blocks another, the blocked object is farther away.
  • Relative height (vertical position in the visual field): higher objects tend to be farther away.
  • Linear perspective: parallel lines appear to converge in the distance; a whole set of cues based on how lines converge.
• Depth cue interrelations example: depth cues affect perceived size and vice versa; size and depth information interact to shape perception.
• The Ponzo illusion (depth-based size illusion): two identical objects placed along converging lines appear different in size because the converging context implies depth.
• The Shepard illusion is another depth-based illusion that interacts with perceived size and depth in a more complex way.
• Escher-style depth illusions illustrate limits of two-dimensional cues to convey three-dimensional structure; the brain’s rules for depth are not infallible.

Size, depth, and context: how depth cues alter size and emotion

• When depth cues indicate one object is farther, it is perceived as larger, even if retinal size is the same as a nearer object (size-Depth interaction).
• Demonstrations where two figures produce the same retinal image but are interpreted differently due to depth cues; the brain’s interpretation can influence perceived size and even perceived emotion (e.g., monsters’ expressions in depth-dependent interpretations).
• Key takeaway: depth cues are not purely geometric; they interact with emotion and interpretation.

Context, culture, and perceptual set

• Contextual influence on perception: the same image can be interpreted differently depending on context, background knowledge, and expectations.
• Cultural context example (perceptual set influenced by environment):
  • Western participants often interpret the elephant image as a group of people in a room with a window.
  • East African participants (more outdoor, basket-on-head culture) tend to see people under a tree with a basket on the head.
  • Both interpretations are valid; perception is shaped by what you are used to perceiving.
• Perceptual set: a predisposition to perceive things in a certain way, often due to prior exposure or expectations.
• Experimental demonstration of perceptual set using ambiguous middle figure (saxophone player vs. woman's face):
  • Two versions of the figure emphasize the saxophone or the face.
  • Participants who saw the saxophone first tended to interpret the middle figure as the saxophone after viewing it; those who saw the face first tended to see the face.
• Takeaway: prior exposure and context bias interpretation of ambiguous stimuli; perception is not neutral.

Implications and transitions: from perception to cognition

• The mind’s interpretation of visual input integrates:
  • Experience and learned rules (e.g., depth cues, grouping rules).
  • Expectations and context (including cultural background).
  • Memory and knowledge that help disambiguate sensory input.
• These ideas foreshadow broader cognitive topics: how we think, learn, store, retrieve, and use information; how biases and mental strategies shape behavior.
• What this means for studying psychology: sensation and perception illustrate that cognitive processes shape even basic experiences like seeing, underscoring the unity of physiology and cognition.

Quick recap: key terms and concepts to remember

• Sensation: physiological recording of stimuli and retinal input.
• Perception: cognitive interpretation and understanding of sensory input.
• Grouping rules (early perceptual organization):
  • Proximity, Similarity, Continuity, Connectedness
• Depth cues: binocular (two eyes) and monocular cues (one eye):
  • Binocular: stereopsis through retinal disparity between eyes.
  • Monocular: relative size, interposition (occlusion), relative height, linear perspective.
• Depth-related illusions: Ponzo illusion, Shepard illusion, and other perspective-based effects.
• Perceptual set: prior exposure biases interpretation of ambiguous stimuli.
• Context/culture: cultural background and environment alter perception of images (e.g., the elephant image).
• Subjective contours and Necker cube: perceptual filling-in and alternative interpretations driven by top-down processing.
• Transition to cognition: understanding thinking, learning, memory, and bias as the next major focus after this perception-focused section.

Exam prep notes: study tips

• Be able to explain the difference between sensation and perception with examples.
• Describe at least four grouping rules and how they affect interpretation of ambiguous images.
• Define binocular vs monocular cues and give two examples of each.
• Explain how depth cues can alter perceived size (size- depth interaction) with a brief example (e.g., Ponzo illusion).
• Discuss how context and culture can alter perception, with the elephant image example.
• Describe the Necker cube and subjective contours as demonstrations of top-down processing.
• Be able to discuss how expectations and memory influence perceptual interpretation (top-down processing).
• Understand how these concepts set the stage for the broader study of cognition in subsequent units.