Sensory, Attentional and Perceptual Processes

Our sense organs function only within a limited range of stimulation:

• Absolute Threshold (AL): The minimum intensity of a stimulus required for detection (e.g., we cannot hear sounds below 20Hz or see light outside the visible spectrum).
• Difference Threshold (DL): Also called the Just Noticeable Difference (JND), it is the minimum change in stimulus intensity required to perceive a difference. If a change is too small, our senses miss it.
• Sensory Adaptation: If a stimulus is constant (e.g., the smell of perfume in a room), our senses adapt and stop registering it after a while.

Attention is the process through which certain stimuli are selected from a group of others for further processing.
Properties:

• Selection: Focusing on specific stimuli while filtering out others.
• Alertness: The readiness to deal with stimuli.
• Concentration: Focusing awareness on certain specific objects while excluding others.
• Search: Looking for a specific subset of objects among many (e.g., finding a friend in a crowd).

Determinants of Selective Attention:

• External Factors: Size, intensity, motion, and novelty of the stimulus (e.g., a moving neon sign attracts more attention).
• Internal Factors: Motivation (hunger makes you notice food), cognitive set (interests), and emotions.

Difference:

Selective Attention	Sustained Attention
Selecting one stimulus among many distractors.	Maintaining focus on one stimulus for a long duration.
Example: Listening to a teacher while ignoring classmates talking.	Example: An air traffic controller watching a radar screen for hours.

Gestalt psychologists (Wertheimer, Köhler, Koffka) proposed that “The whole is greater than the sum of its parts.”
They argued that we do not perceive the world as fragmented sensory bits but as organized, meaningful configurations (Gestalts). This organization follows laws like Figure-Ground segregation, Proximity, Similarity, and Closure.

Space perception creates our 3D world (distance, depth, and height) from 2D retinal images. It occurs through a combination of:

• Monocular Cues: Depth cues available to a single eye (e.g., relative size).
• Binocular Cues: Depth cues requiring both eyes (e.g., convergence).
• Motion Parallax: The relative movement of objects as we move (closer objects move faster).

Monocular Cues (Pictorial Cues):

• Linear Perspective: Parallel lines converge in the distance (like railway tracks).
• Relative Size: Smaller objects appear farther away.
• Interposition: An object blocking another is seen as closer.
• Texture Gradient: Texture becomes denser and less distinct as distance increases.

Binocular Cues:

• Retinal Disparity: Because eyes are ~6.5cm apart, they see slightly different images. The brain fuses these to calculate depth.
• Convergence: Eyes turn inward to focus on near objects. The muscle tension gives depth information to the brain.

Illusions are “misperceptions” resulting from the misinterpretation of sensory information. They occur because:

• Universal Tendencies: Our brain tries to apply 3D rules to 2D images (e.g., Müller-Lyer illusion).
• Context: The surrounding environment distorts our judgment of size or shape.
• Experience: People from “carpentered” environments (cities with right angles) are more prone to certain geometric illusions than those from rural environments.

Perception is not just biological; it is learned.

• Cultural Needs: People perceive what is valuable in their culture faster (e.g., Eskimos have many words for snow and perceive variations others miss).
• Environment: Africans living in dense forests (with no open horizons) may perceive distant objects as “small” rather than “far” because they lack experience with vast distances.

(Guidance for Student Activity)
When collecting ads, note how they use:

• Attentional Factors: Use of bright colors (Intensity), large fonts (Size), or celebrity faces (Interest) to break through the clutter.
• Perceptual Factors: Using Closure (incomplete slogans you mentally finish) or associating the product with high status (Halo Effect).

(Guidance for Experiment)

• Haptic Perception (Touch): Visually challenged children build a mental image part-by-part (sequential). Their drawings/descriptions will emphasize texture, weight, and key features (trunk, tail) rather than perspective.
• Visual Perception: Sighted children grasp the “whole” immediately (simultaneous). Their drawings will emphasize visual outline and 2D perspective.
• Conclusion: Perception is multimodal. While vision integrates instantly, touch integrates sequentially, leading to different internal representations of the same object.