Module 3: Perception

Sensation vs. Perception

• Sensation: The process of receiving external stimuli through sensory receptors.

• Perception: The cognitive process of interpreting what is sensed, allowing us to understand our environment. This process builds upon the sensory input and elaborates it into a comprehensive interpretation.

Constructivist vs. Ecological Views

• Constructivist View: Proposes that perception is constructed through cognitive processes, emphasizing the role of mental interpretation and context.

• Ecological View: Suggests that perception is inherently linked to a rich environmental structure that can be processed directly, with both traditional (direct perception with no mental processing) and modern (involving cognitive complexity) perspectives.

Neural Bases of Visual Perception

Structure of the Eye

• Light enters through the cornea, passes through the pupil (controlled by the iris), and is focused by the lens onto the retina.

• The retina contains photoreceptors that convert light into neural signals: cones (for color and detail, primarily located in the fovea) and rods (sensitive to light and motion but color-blind, located in the periphery)

Visual Pathway from Retina to Cortex

1. Optic Nerve: Transmits visual information from the retina.

2. Thalamus: Acts as a relay station for sensory information before reaching the cortex.

3. Primary Visual Cortex (V1): Located in the occipital lobe, responsible for initial visual processing.

4. Secondary Cortical Areas: Further processing occurs in areas associated with visual perception, with parallel processing pathways identified as the:

   • Occipital-Parietal Pathway (where): Involved in spatial processing.

   • Occipital-Temporal Pathway (what): Involved in object recognition.

Organizing the Visual Scene into Objects

1. Perceptual Grouping

• The challenge of organizing visual stimuli into distinct objects involves understanding which elements group together and which do not.

• Gestalt Principles: Provide rules on how objects are perceived together, emphasizing higher-level organizational principles:

  • Pragnanz (Simplicity): Visual inputs are interpreted in the simplest way.

  • Similarity: Objects that are similar tend to be grouped together.

  • Parallelism & Symmetry: Shapes that are parallel or symmetrical are likely seen as part of the same object.

  • Proximity: Closer objects are seen as forming a group.

  • Common Fate: Objects moving in the same direction are grouped.

2. Figure-Ground Organization

• This involves segregating a visual scene into a foreground (figure) and background (ground).

• Factors that influence figure-ground assignment include geometric cues such as size, symmetry, and familiarity.

Conclusion

Understanding perception involves unpacking both the physiological foundations and the cognitive processes that allow us to make sense of sensory information. The interplay between sensation and perception, combined with our environment's richness, creates our perception of the world around us.