Lecture 3 (Perception).ppt
Transcript
Basics of Perception Lecture 3 Overview of Major Topics • • • • • Visual Perception Pattern Recognition Object Recognition Agnosia Auditory Perception Is our perception veridical? • Quite often we perceive things that do not exist and misperceive or even fail to perceive things that do exist. •...
Basics of Perception Lecture 3 Overview of Major Topics • • • • • Visual Perception Pattern Recognition Object Recognition Agnosia Auditory Perception Is our perception veridical? • Quite often we perceive things that do not exist and misperceive or even fail to perceive things that do exist. • Perception does not provide a veridical treatment of our physical world. Simons and Levin (1998) Sensation versus Perception • Sensation: The reception of energy from the environment, and its initial encoding into the nervous system. • Perception: The process of interpreting and understanding sensory information. Visual Perception The Fovea • Light that we directly focus on lands in the Fovea. • Contains almost all cones. • Acuity -- accurate, precise vision-- is best in the fovea. • Rods are abundant at the sides (periphery) of the fovea. Compression • Transformation that both analyzes and summarizes the original input (e.g., visual, auditory, tactile, etc.). • As light passes through the eye, information is lost because it is reflected off of the many cells at the back of the eye. • In peripheral vision, there are many-to-one synapses from the rods and cones to the bipolar cells, and from the bipolar to the ganglion cells. • By the time neuronal information reaches the visual cortex, the visual information has been preprocessed, thus providing a summerized record of the actual visual stimulus. Gathering Visual Information • Saccades: Rapid eye movements. Last between 25 and 100 msec. • Fixations: Pauses between saccades. The eye takes in visual information during fixations. Measuring Eye Movements • Huey (1908): plaster of Paris cup placed on cornea. Cocaine was used to make the cornea surface insensitive to the cup. A light rod was attached to the cup. It was sensitive to any movement. Eye movements were recorded on paper, which rotated with a moving drum. New Methods of Eye Tracking • Infrared cameras can lock onto infrared “sinks”. • Importantly for contemporary eye-tracking researchers, the pupil provides a very good infrared sink. • The infrared camera then follows the eye as it traverses a predefined visual space. • We measure: fixations, gaze durations, gaze location. Infrared Light Source Eye Tracker Visual Sensory Memory • Also known as Iconic Memory. • Visual persistence: The apparent persistence of a visual stimulus beyond its physical duration (To demonstrate: Rapidly wobble a pencil between two fingers). Initial Storage and Duration • Iconic memory is very brief. • We have little “intuitive” insight into the operation of iconic memory (i.e., it operates without conscious awareness). • Sperling conducted several tachistoscopic studies aimed at detailing the amount and duration of iconic memory. Sperling’s Experiment Sperling’s Experiment (Overview) • Used a tachistoscope to rapidly present images to the eyes. • Subjects saw a 3 x 4 grid of letters, presented very briefly (50 ms). • In the whole report condition, subjects had to free recall the letters. • Whole report performance was poor (about 37% accuracy). Cue delays from 5-500ms did not affect performance. • Span of apprehension. Sperling’s Experiment (Continued) • In the partial report condition, a tone was sounded right after the letter grid disappeared. • A high pitch tone cued recall of the top row; a medium pitch tone cued recall of the middle row; a low pitched tone cued recall of the bottom row. • Partial report accuracy was at 76%. Sperling’s Experiment (Conclusion) • Why did Sperling argue that decay rather than interference is the loss mechanism in iconic memory? • How long does information remain in iconic memory? Averbach and Coriell (1961) • Presented two rows of eight letters each. • Used a visual cue, above or below the to-berecalled letter. • The circle-maker cue “masked” perception of the letter. • Backward Masking: When a later visual stimulus affects perception of an earlier one. Ecological Validity and the Icon • Haber (1983) • The icon is irrelevant to real-world perception. • Data are useful only if “reading in a thunderstorm.” • Criticisms of Haber? o Philosophical o Experimental Models of Pattern Recognition • The Template approach • Feature analysis / Feature detection o (a feature is component of a pattern that can co-occur with other features) o Connectionism o Recognition by components Pandemonium Pandemonium Selfridge (1959) • Types of Demons: Data / Image Computational / Feature Cognitive Decision Pandemonium’s Weakness • Complete bottom-up processing Context Effects • Data Driven (bottom-up) Processing is driven by the stimulus. • Conceptually Driven (top-down) Processing is driven by higher level knowledge. Examples of Top-Down Processing Connectionism • Back Propagation • Delta Rule • Distributed Representation • Local Minima • Massively Parallel Processing • Input Units • Hidden Units • Output Units Recognition by Components Biederman (1987) • Geons: building blocks of visual objects. • Data on Non-recoverable Drawings. • Limitations of the model: Over-reliance on data-driven processes? Whole versus part perception? Neuropsychological evidence? Agnosia • Failure or deficit in recognizing objects. • Examples: Prosopagnosia (faces) Apperceptive Agnosia (patterns) Associative Agnosia (meanings) Audition Auditory Sensory Memory • Also known as Echoic memory: a brief memory system that receives auditory stimuli and preserves them for some amount of time. • Studying ASM: Three-eared man technique Modality Effect Suffix Effect Echoic Memory: Initial Storage and Duration • Darwin, Turvey, and Crowder (1972) developed a “three-eared man procedure”. • Nine separate stimuli were presented. • Whole-report condition: 37% correct • Partial-report condition: > 50% correct • The partial report superiority was evident over delays lasting 4 seconds. Auditory Persistence and Erasure • Redirected attention • Persistence: Crowder and Morton (1969) o Visually presented 9 digits o Three conditions: silent vocalization, active vocalization, passive vocalization. o For the last 3 items in the list, participants in the active and passive vocalization groups produced fewer errors. o Interpretation: the active and passive vocalization groups could rely on echoic memory. Auditory Pattern Recognition • Templates --the problem of invariance? • Feature Detection • Conceptually Driven Processing --Warren and Warren’s (1990) study Conceptually Driven Processing • Warren and Warren (1970) presented sentences to participants that contained a word with a missing phoneme (i.e., a minimal, meaningless primitive of language). • The missing phoneme made the word ambiguous. • However, participants reported hearing the word that fit the appropriate context of the sentence. - The End -
