Top-down processing refers to perception that is driven by cognition, expectations, and prior knowledge rather than just raw sensory input. When an individual is told that a figure-ground image is reversible, their brain actively searches for the alternative interpretation based on that instruction. This demonstrates how mental sets and expectations shape our sensory experience, proving that perception is an active, constructive process rather than a passive recording of the environment.

The Mueller-Lyer illusion is a classic geometric-optical illusion. It consists of two lines of identical length that appear to be different sizes because of the orientation of the arrowheads at their ends. This illusion is frequently used in psychology to demonstrate how top-down processing and context influence our perception of reality.

Optical illusions arise when the brain misinterprets sensory input. While sensation is the raw detection of stimuli, perception is the cognitive process of organizing and interpreting that data. Illusions occur because our perceptual systems use heuristics that can lead to systematic errors in interpretation.

Blindsight is a phenomenon observed in patients with damage to the primary visual cortex. While they report being blind, they can still respond to visual stimuli in their 'blind' field, such as identifying shapes or movements, because the brain's subcortical pathways remain intact and process visual information unconsciously.

The principle of nearness, or proximity, suggests that objects that are close to one another in space are perceived as a single group or unit. This is a fundamental rule of Gestalt psychology, which explains how the brain organizes visual elements into meaningful patterns rather than seeing them as isolated parts.

The visual angle is the angle that an object subtends at the eye, which is a critical factor in determining the size of the image on the retina. Note: The provided answer 'Obsolute angle' appears to be a misspelling or non-standard term; 'Visual angle' is the correct psychological term.

Selective attention is the cognitive ability to focus on specific stimuli in the environment while ignoring irrelevant or distracting information. This mechanism is essential for processing complex sensory input and allows individuals to maintain focus on tasks despite the presence of competing auditory or visual stimuli.

Human attention is highly sensitive to change. When a stimulus remains constant, the sensory system often undergoes adaptation, leading to a decrease in responsiveness. However, a sudden change or alteration in the environment acts as a signal that something new or potentially significant has occurred, which naturally draws our focus. This mechanism is an evolutionary adaptation that helps organisms remain alert to potential threats or opportunities in their surroundings.

Studies on visual search training demonstrate that while individuals can acquire and implement new search strategies, the efficacy of these strategies is context-dependent. Specifically, performance gains are often observed in target-present conditions, but these improvements may not generalize to target-absent conditions, where the search process remains fundamentally different. This highlights the limitations of training in overcoming specific cognitive constraints in visual search tasks.

Cubism, pioneered by artists like Pablo Picasso and Georges Braque, revolutionized visual art by deconstructing objects into their basic geometric components. By analyzing and reassembling these features from multiple viewpoints simultaneously, Cubist artists moved away from traditional perspective. This approach mirrors the psychological concept of feature analysis, where complex stimuli are broken down into simpler, fundamental elements to facilitate recognition and cognitive processing of the visual scene.