Key Points

Sensation is the initial experience of a stimulus registered by a sense organ. Humans have seven sense modalities: five external (vision, hearing, smell, taste, touch) and two deep senses (kinesthetic and vestibular).

Absolute Threshold (AL) is the minimum stimulus value needed to activate a sensory system. Difference Threshold (DL) is the smallest difference between two stimuli required to notice them as different.

Attention is the process of selecting certain stimuli from a group of others. Its key properties include alertness (readiness to deal with stimuli), concentration (focusing awareness), and search (looking for specific objects).

Selective attention is focusing on a limited number of stimuli. Sustained attention (vigilance) is maintaining focus for a long duration. Divided attention is attending to more than one thing at once, usually with practiced, automatic tasks.

External factors relate to stimulus features like size, intensity, and novelty. Internal factors are within the individual, such as motivational needs (hunger) and cognitive factors (interest, attitude).

Broadbent's Filter Theory suggests a bottleneck where only one stimulus passes. Triesman's Filter-Attenuation Theory proposes unattended stimuli are weakened, not blocked. Johnston and Heinz's Multimode Theory suggests selection can happen at different stages.

The span of attention is the number of objects one can attend to in a brief exposure. Miller identified this as the 'magic number' seven, plus or minus two (5 to 9 items).

Perception is the process by which we recognize, interpret, and give meaning to sensory information. Unlike sensation, it is an active process of constructing our understanding of the world.

Bottom-up processing starts with stimulus features and builds to a whole perception. Top-down processing begins with the whole, using our knowledge and expectations to identify components.

The perceiver's motivation, expectations (perceptual sets), cognitive style (field dependent vs. independent), and cultural background significantly influence how they interpret stimuli.

Gestalt psychologists proposed that we perceive objects as organized wholes, not discrete parts. The most basic form of this is figure-ground segregation, where an object (figure) stands out from its background.

Key laws include Proximity (grouping nearby items), Similarity (grouping similar items), Continuity (perceiving continuous patterns), and Closure (filling in gaps to see a complete figure).

Monocular cues allow depth perception with one eye and are used in art. They include relative size, interposition (overlapping), linear perspective, aerial perspective, and texture gradient.

Binocular cues require both eyes to perceive depth. They include Retinal Disparity (difference between images in each eye), Convergence (inward turning of eyes for near objects), and Accommodation (lens focusing).

Perceptual constancy is the tendency to perceive objects as stable and unchanging despite changes in sensory input. This includes size constancy, shape constancy, and brightness constancy.

Illusions are misperceptions resulting from the misinterpretation of sensory information. Examples include geometrical illusions like the Muller-Lyer illusion and the apparent movement illusion known as the phi-phenomenon.

Cultural experiences and environment shape perception. Studies show people from different cultures vary in their susceptibility to certain illusions (e.g., Muller-Lyer vs. Vertical-Horizontal) and in interpreting pictures.

ADHD is a behavioural disorder in children characterized by inattention, hyperactivity, and impulsivity. It is a disorder related to difficulty in sustaining attention.