This unit covers the fundamental concepts of sensation and perception, exploring how raw sensory data is interpreted by the brain. It distinguishes between bottom-up and top-down processing, examines various aspects of attention and apparent movement, and introduces Gestalt principles. Students should be prepared to differentiate between binocular and monocular depth cues, and understand the different types of perceptual constancy.
Sensation and Perception Introduction
Defines sensation as raw data detection and perception as sensory information interpretation.
This unit, presented by Mr. Luke, introduces Cognition through the foundational concepts of sensation and perception.
Sensation is the raw input, while Perception is the brain's processing of that input.
| Sensation (Detection) | Perception (Interpretation) | |
|---|---|---|
| Definition | The raw data or information received from our sensory receptors. | The process of interpreting the information we obtain through our 5 senses. |
| Role | Focuses on the initial detection of stimuli. | Focuses on making sense of detected sensory information. |
| Key Sense | Involves all sensory receptors. | Especially significant for vision. |
Bottom-Up vs. Top-Down Processing
Explains how perception is built from sensory data or influenced by prior knowledge.
Bottom-Up processing builds perception from raw data, while Top-Down uses existing knowledge.
| Bottom-Up Processing | Top-Down Processing | |
|---|---|---|
| Stimuli Type | For unfamiliar or complex stimuli. | For familiar or simple stimuli. |
| Mechanism | Perception built from the ground up, interpreting sensory information as it enters. | Uses prior knowledge and experiences to interpret the information. |
| Reliance on Knowledge | Without relying on prior knowledge or expectations. | Using prior knowledge and experiences. |
| Example | Watching a new mystery movie like MEMENTO, trying to identify the perpetrator solely based on clues, like the protagonist. | The Proof Reader's Illusion, where you auto-correcting mistakes because you know what you wrote. Solution: peer-review or reading it out loud. |
| Strength/Weakness | We are often surprised by twist endings because we rarely rely solely on this. | Strength: Efficient and quick processing. Weakness: Sometimes it can lead us astray. |
Concept
Perceptual Set
A mental shortcut (like tinted glasses) your brain uses to quickly interpret experiences, leading to immediate perception based on our expectations or emotions.
Concept
Skewed Perception
How existing prior knowledge and expectations shape the perception of new information. Influenced by internal factors and external factors such as culture, mood, emotion, expectation, and environment.
The Müller-Lyer illusion demonstrates how culture and depth cues influence perception. In cultures where right (90°) angles are common, the line with outward pointing fins is perceived as longer than the line with inward pointing fins. This occurs because our brain interprets these shapes using depth cues, where outward fins resemble a 'far' corner and inward fins a 'near' corner, making objects perceived as farther away appear longer.
Attention
Covers how we focus on stimuli and how our attention can fail.
Attention plays an important role in our perception, determining what stimuli we process.
Selective Attention focuses on one stimulus, while the Cocktail Party Effect describes background monitoring.
| Selective Attention | Cocktail Party Effect | |
|---|---|---|
| Mechanism | When we focus on a particular stimulus, we often tune out other stimuli in our environment. | Our brain continues to monitor the background for relevant information or personal information. |
| Example | Engaging in a conversation at a party, ignoring other background noise. | Even if not actively paying attention, you notice when somebody nearby mentions your name. |
Concept
Inattentional blindness
Occurs when our attention is divided, causing us to fail to notice stimuli in our visual field because our attention is focused elsewhere.
Concept
Change blindness
Our failure to notice changes in an environment or visual scene.
Apparent Movement and Illusions
Describes perceiving motion when none exists and various visual illusions.
Concept
Apparent Movement
The perception of motion even though nothing is actually moving, especially for objects in our peripheral vision.
Concept
Autokinetic Effect
A stationary point of light in a dark environment appears to move because the brain and eyes have difficulty maintaining stable perception without a visual reference.
Concept
Induced Movement
A stationary object appears to move due to the motion of surrounding objects.
Concept
Phi Phenomenon
The perception of a single, moving image when stationary images (like flashing dots or light blinking) are presented in rapid succession.
Concept
Stroboscopic motion
The illusion of movement created by showing a series of images in rapid succession, forming the basis of Animation.
Gestalt Psychology and Principles
Explains how the brain organizes sensory information using six Gestalt principles.
Concept
Gestalt Psychology
A school of thought explaining how the brain organizes, identifies, and interprets sensory information from the environment to understand and make sense of it, often involving the Temporal lobe.
Gestalt Principles
How humans naturally group elements together to form meaningful patterns.
Similarity
Grouping similar elements together.
Proximity
Grouping nearby objects as a single unit.
Continuity
Preferring to perceive continuous patterns or lines.
Closure
Subconsciously filling in missing information to complete incomplete figures.
Figure and Ground
Separating the object of focus (figure) from its background.
Symmetry
Perceiving symmetrical objects as one cohesive unit rather than separate parts.
Similarity groups like elements, while Anomaly highlights unique ones.
| Similarity | Anomaly | |
|---|---|---|
| Principle | We perceive a group of similar objects or patterns as one cohesive unit. | When an object is different from the others, it becomes the focal point and stands out. |
Figure and Ground describes how our visual system separates objects from their surroundings.
| Figure | Ground | |
|---|---|---|
| Role | The object of focus in our visual field. | The background against which the figure is perceived. |
Depth Perception
Details perceiving relative distance using binocular and monocular cues.
Concept
Depth Perception
The ability to perceive the relative distance of an object in one's visual field, utilizing both Binocular Cues and Monocular Cues.
Binocular cues use both eyes, while monocular cues can be perceived with one eye.
| Binocular Cues | Monocular Cues | |
|---|---|---|
| Eyes Used | Require the use of both eyes. | Can be perceived with one eye. |
| Application | Primarily for perceiving depth in 3D space. | Allows perception of depth on flat or 2D surfaces. |
Concept
Convergence
A binocular cue where our eyes turn inward to focus on close objects.
Concept
Accommodation
A binocular cue involving the changing shape of the eye's lens to focus on objects at different distances.
Concept
Retinal Disparity
A binocular cue where each of our eyes sees a slightly different view of the object (left retinal image vs. right retinal image), which the brain uses to perceive depth.
Monocular Cues (perceived with one eye):
Concept
Relative Motion
As we move, objects that are actually stable may appear to move. If you fix your gaze on a fixation point, objects beyond the fixation point will appear to move with you. Objects in front of the fixation point will appear to move backward. The farther an object is from the fixation point, the faster it will seem to move.
Concept
Motion Parallax
A monocular cue where objects closer to you appear to move quickly, while those that are farther away seem to move more slowly. E.g., when driving cars, nearby landscapes move fast, while clouds appear to move slowly.
Perceptual Constancy
Explains the brain's ability to perceive objects as consistent despite appearance changes.
Concept
Perceptual Constancy
The brain's ability to perceive objects as having consistent shape, size, color, and lightness, even when their appearance changes due to varying viewing conditions.
Concept
Size Constancy
The brain's tendency to perceive objects as the same size, even while our distance from them varies. Perceiving an object's distance provides cues to its size.
Concept
Shape Constancy
The tendency of the brain to perceive an object's shape as the same, even when it moves or its orientation changes. The Tabletop Illusion is an example of misapplied shape constancy.
Concept
Color Constancy
Our ability to perceive the color of an object to remain consistent, even if the lighting changes.
Concept
Light Constancy
Our ability to perceive the blackness, whiteness, and grayness of an object as consistent even when different lighting conditions (e.g., shading) affect its appearance.
Lightness Illusion
Despite being perceived as lighter, Square B on a checkerboard with a cylinder casting a shadow is actually identical in lightness to Square A. This highlights how our brain adjusts for perceived lighting conditions.