Chapter 3: Sensation and PerceptionSensation: activity of receptor organsPerception: interpretation of sensory system activity

Visual system organization: Each eye projects to both left and right hemisphere. Same half of each retina monitors opposite visual field

Eye

Retina and photoreceptors

Rods:125 mil; low light; color blind; peripherally located

Cones:7mil; daylight; color vision; centrally located

Gathering visual information• When scanning a visual scene (such as the picture on the left) or reading text (right), they

engages in jerky, jumping movements called saccades. • Ave fixation = approx. 250/ms; Ave saccade = 25-175/ms; visual suppression during saccade• Change blindness: failure to detect visual changes during saccade• Inattention blindness: failure to detect signal due to inattention, despite visual fixation• Focal attention: processing object features during fixation (object interpretation)• Trans-saccadic memory: coordinating objects across fixations to build up overall scene

Span of Apprehension: How much info gathered in brief glance at visual pattern? Iconic memory

• Early studies: 4.5 unconnected letters; whole report technique; ‘reading off visual icon’

• 1960 Partial report technique of George Sperling

Pattern Recognition: Perceiving meaningful objects

Gestalt Organizing Principles: Stimulus information combined with innate organizing principles of sensory systems. Need examples of principles (proximity, similarity, common fate, closure, and overriding principle of Pragnanz

Stored canonical view: Evidence for Template approach

Template matching

• But what about K K K K K K

Selfridge (1959) Pandemonium model: Example of Feature Analysis Approach

Parallel Processing of critical features and feature combinations

Physiological evidence for FA

Hubel and Wiesel find feature detectors in occipital lobe of cat

Connectionist (PDP) word recognition model

Feature analysis model based more closely on brain function. Both top-down (incorporating context effects) and bottom up (critical features) influences. Three layers, input (features), hidden (feature combo), and output (meaningful pattern)

Highly interconnected with varied + and – weighted connections between nodes

Recognition by Components

• Meaningful forms base on combinations of primitive “geons”.• Geon: simple 3D geometric forms • Intersections are most informative of geon• Evidence: recoverable vs. non-recoverable forms

Weakness: very bottom-up; expertise effects (experts don’t show same non-recoverable effects as novices) and context effects (non-recoverable can be overcome by context)

Visual Agnosia: failure of object recognition

Prosopagnosia: inability to recognize familiar faces associated with damage to fusiform gyrus of temporal lobe

Apperceptive agnosia: inability to coalesce features into meaning whole (object or form). RH/parietal lobe malfunction

Associative agnosia: unable to associate form with meaning or identity. Ex: can define form (hammer is to pound) but cannot identify hammer form. Temporal visual stream damage and corpus collosum

Audition: the ear

Mechanical function based on incoming vibrations. Higher frequencies processed nearer the base of cochlea, lower nearer the apex.

Auditory Sensory Memory

• “Three eared man” studies. Whole report = little over 4 items, partial = early 5, partial advantage maintained with 4 sec delay. Because of longer lasting echo memory, modality effect: better memory for end of list items if presented auditorily compared to visually.

Conceptually driven auditory perception: phonemic restoration effect