Summary

This presentation covers the basics of perception, including visual and auditory perception. It discusses topics like visual persistence, Sperling's experiment, and models of pattern recognition.

Full 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 -

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