Answer to Question 1
Bottom-up processing can account for how we recognize general instances of chairs, lamps, and faces and so on, but it does not adequately explain how we recognize particular chairs or particular faces.
Answer to Question 2
Both top-down and bottom-up processing approaches have garnered empirical support. On one level, the constructive-perception theory, which is more top-down, seems to contradict direct-perception theory, which is more bottom-up. Constructivists emphasize the importance of prior knowledge in combination with relatively simple and ambiguous information from the sensory receptors. In contrast, direct perception theorists emphasize the completeness of the information in the receptors themselves. They suggest that perception occurs simply and directly. Thus, there is little need for complex information processing.
Sensory information may be more richly informative and less ambiguous in interpreting experiences than the constructivists would suggest. But it may be less informative than the direct-perception theorists would assert. Similarly, perceptual processes may be more complex than hypothesized by Gibsonian theorists. This would be particularly true under conditions in which the sensory stimuli appear only briefly or are degraded. Degraded stimuli are less informative for various reasons. For example, the stimuli may be partially obscured or weakened by poor lighting. Or they may be incomplete, or distorted by illusory cues or other visual noise (distracting visual stimulation analogous to audible noise). We likely use a combination of information from the sensory receptors and our past knowledge to make sense of what we perceive.
Timber in storage for later processing at a sawmill.
Top to bottom: tiger, lion, jaguar, and leopard.
Overview of RNA processing and posttranscriptional gene control
rRNA processing
The perception of motion under four different conditions.
Exogenous Antigen Processing