.png){kind=icon}
Chapter Summary
This chapter introduces the field of perception: the process by which sensory information is pro-cessed to create our conscious experiences of the environment and to guide our actions. The primary focus of the chapter is on visual perception. Visual perception begins when light passes through the cornea and pupil. The light is then focused by the lens on the retina which is at the back of the eye and the retina contains light receptors known as photoreceptors. The photoreceptors convert the light energy into neural signals that are transmitted to various regions of the brain including the primary visual cortex, which is located at the back of the brain. Different regions of the brain process different aspects of visual information. For example, the ventral, or “what,” pathway projects from the primary visual cortex to the inferior temporal lobe, and this pathway aids in our identification of objects (i.e., “what” they are). The dorsal, or “where,” pathway projects from the primary visual cortex to the parietal lobe, and it provides us with information pertaining to the spatial location of an object and guides our interactions with an object. Visual perception is a complex process, and many regions of the brain are involved. As one example, an area in the temporal lobe known as the fusiform face area (FFA) is important for processing faces. Damage to the FFA can result in difficulty recognizing faces which is known as prosopagnosia. Another area in the temporal lobe is involved in recognizing places and it is known as the parahippocampal place area (PPA).
Perceptual processes are often divided into two major, complementary types of processing: bottom-up (data-driven) processing (or influences) and top-down (user-driven) processing (or influences). Bottom-up processing refers to the contribution of the physical features of the stimulus to our perceptual experience (e.g., RBC). Top-down processing, on the other hand, relates to perception that is influenced by goals, expectations and prior knowledge. The interaction of top-down and bottom-up processing leads to perception as how we understand perception. The empirical theory of colour vision highlights this as we use prior knowledge of how objects look under certain lighting, as well as bottom-up processing in order to perceive colour.
The first part of the chapter focuses on the ventral stream and examines several theories of pattern recognition. Pattern recognition, the ability to recognize an event as an instance of a particular category of event, has been of interest to researchers in cognitive psychology and forms the basis of theories of perception. These theories focus on how internal representations of objects are formed. Many bottom-up theories arose from pattern recognition, which itself was based on two theories: template-matching theory (multiple-trace memory model, Posner experiments) and feature detection theory (the pandemonium model). Biederman offered yet another theory, known as the recognition-by-components theory (RBC), which explains how we rapidly recognize objects based on their constituent, basic, three-dimensional elements (geons).
Detecting individual features can be influenced by context and prior knowledge. The word superiority effect is a prototypical example of this type of processing, as is the jumbled word effect. Even the perception of colour can be influenced by context (Purves and Lotto experiments). Con-textual effects also apply to cross-modal conditions, exemplified in the McGurk effect. Aside from bottom-up and top-down hypotheses, Gestalt psychology was also an influential perspective on the topic of perception processing. The Gestalt approach emphasizes that “the whole that is perceived is greater than the sum of its parts.” Gestalt psychologists formulated principles of perceptual grouping based on experience, similarity, proximity, symmetry, parallelism, and common movement.
The focus of the chapter then switches to the dorsal stream and review of evidence that demonstrates the importance of the dorsal stream in perception and action. A case study of a patient with a condition known as optic ataxia (i.e., inability to reach for objects) is discussed. Gibson posits a theory of ecological optics, which emphasizes the importance of action when considering the goal of perception resulting from direct contact with environmental energy. In this theory, importance was placed on how environmental information stimulates the senses. The ambient optical array is all the visual information that is present from a particular viewpoint. The gradient of texture density, topographical breakage, and scatter-reflection are principles that give us useful information about objects in our environment. As an observer moves through his/her environment, the change in optical information is referred to as transformation.
The last portion of the chapter focuses on multimodal perception, which involves at least two sensory systems working together rather than a single sensory system (such as vision). Although in-formation processed by multiple sensory systems can easily be integrated in most situations, the modality appropriateness hypothesis posits that when there is competition among multiple sensory systems, a dominant modality will process specific types of stimuli. The interaction between vision and audition (hearing), vision and touch, and finally multimodal perception and taste are outlined.
Chapter Objectives
- To describe the basic physiology of visual perception.
- To outline basic facts about perception learned from the visual deficits of patients with brain damage.
- To describe how objects are consciously perceived and recognized.
- To illustrate the importance of context and observer knowledge in theories of perception.
- To examine the relation between perception and action.
- To explore the nature of multimodal perceptions.