3.1-3.2: Introduction to Sensation & Perception 

SENSATION

• To represent the world, we must detect physical energy (stimulus) from the environment and convert it into neural signals, a process called Sensation.
• When we select, organize, and interpret our sensations, the process is called Perception.

BOTTOM-UP PROCESSING:

• Analysis of the stimulus begins with the sense of receptors and works up to the level of the brain and mind.

TOP DOWN PROCESSING:

• Information processing guided by high level mental processes as we construct perceptions drawing on our experience and expectations.

THRESHOLDS:

• Absolute Threshold - Minimum stimulation needed to detect a particular stimulus 50% of the time.
• Difference Threshold - Minimum difference between two stimuli required for detection 50% of the time, also called Just Noticeable Difference (JND)
• Weber’s Law - The size of the JND is proportional to the intensity of the stimulus AKA.. if the stimulus intensity is high, the JND will be large (it will take a bigger chance to tell the difference), and vice versa..
• Subliminal Threshold/Messaging - When stimuli are below one’s absolute threshold for conscious awareness. In other words for most people these items are not consciously detected. However, it is possible that some will notice these items! Studies have found that subliminal words flashed briefly on a screen can “prime” a person’s later responses, but will NOT impact a large groups buying habits.
• Signal Detection Theory - Simply put, it states that our thresholds are not absolute, they change. It predicts how and when we detect the presence of a faint stimulus (a signal) amidst background noise (other stimulation). It also assumes that there is no signal absolute threshold and detection depends on experience, expectations, motivations, and level of fatigue.

SENSORY ADAPTATION:

• Describes the instance where there is a diminished sensitivity as a consequence of constant stimulation. Examples would be wearing a bandaid, jewelry, glasses, or getting into a cold pool.
• Depth Perception: Depth perception enables us to judge distances, Gibson and Walk (1960) suggested that human infants (crawling age) have depth perception. Even newborn animals show depth perception.
• Sensory Deprivation: Also known as perceptual isolation, suggests that vision is at least partly on acquired taste.

GESTALT PSYCHOLOGY:

• Helps us organize information into meaningful wholes, but remember “a whole is not simply the sum of its parts”.

• Gestalt Grouping - Having discriminated figure from ground, our perception needs to organize figure into a more meaningful form using grouping rules. This can be divided into six sectors, known as the Gestalt Principles.

• Figure Ground - Your brain distinguishes between the objects it considers to be it considers to be in the foreground of an image (the figure, or focal point) and the background (the area on which the figures rest).

  

• Similarity - they can be used to tie together elements that might not be right next to each other in a design, they can be grouped by color, shape, or size.

  

• Continuation - The law of continuity posits that the human eye will follow the smoothest path when viewing lines, regardless of how the lines were actually drawn, this can be a valuable when the goal is to guide a visitor’s eye in a certain direction.

  

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• Proximity - refers to how close elements are to one another. The strongest proximity relationships are those between overlapping subjects, but just grouping objects into a single area can also have a strong proximity effect.

  

• Closure - The idea that your brain will fill in the missing parts of a design or image to create a whole. In its simplest form, the principle of closure allows your eye to follow something like a dotted line to its end.

  

• Symmetry/Order - States that your brain will perceive ambiguous shapes in as simple a manner as possible. For example, a monochrome version of the Olympic logo is seen as a series of overlapping circles rather than a collection of curved lines.

  

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MONOCULAR v BINOCULAR CUES

MONOCULAR:

• Interposition: Objects that occlude (block) other objects tend to be perceived as closer.
• Linear perspective: Parallel lines like railroad tracks, appear to converge with distance. The more the lines converge, the greater their perceived distance.
• Relative Size: If two objects are similar size, we perceive one that casts a smaller retinal image as farther away.
• Texture Gradient: Indistinct (fine) texture signals increasing distance.

BINOCULAR:

• Convergence: When two eyes move inward (towards the nose) to see near objects, and outward (away from the nose) to see far away objects…object is perceived as closer the more eyes turn inward.
• Retinal Disparity: Images from the two eyes differ..the greater the difference between the two objects, the closer the object.

PERCEPTION OF MOVEMENT

• Stroboscopic motion: our tendency to perceive motion in a rapid series of slightly varied still images in rapid succession.
• Phi Phenomenon: When lights flash at certain speed they tend to present illusions of motion. Neon signs use this principle to create motion perception.

CONSTANCY & SIZE-DISTANCE

CONSTANCY:

• Size Constancy: Stable size perception amid and changing size of stimuli.
• Perceptual Constancy: Perceiving objects as unchanging even as illumination and retinal image change. Perceptual constancies include constancies of shape and size.

SIZE-DISTANCE:

• Moon Illusion: It appears larger and farther away when on the horizon (smaller and closer when up in the night sky)
• Ponzo Illusion: when we use background objects to detect an object's distance.

PERCEPTUAL ADAPTATION & PERCEPTUAL SET

• Adaptation: Visual ability to adjust to an artificially displaced visual field, e.g prism glasses.
• Set: A mental predisposition to perceive one thing and not another… a tendency to perceive or notice some aspects of the available sensory data and ignore other.

SCHEMA

• The list of characteristics of an object (concept), that allows us to categorize future, unfamiliar information.
• It allows us to know the difference between objects, (i.e chair versus a desk), and they develop through experience.
• They influence how we perceive future, unfamiliar information

CONTEXT

• Cultural Context: Context instilled by culture also alters perception.
• Context Effects: A given stimulus can evoke radically different perceptions, based on the immediate context of the stimulus.

MOTION PARALLAX

• Describes a neurological illusion
• Brain takes in cues from the eye i.e passing trees, lines on the road, size of objects, etc. The brain is then fooled into thinking objects that are further are moving slower.

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