psychology of visual perception C O M M U N I C A T I O N D E S I G N, A N I M A T E D I M A G E 2014/2015

Transcription

1 psychology of visual perception C O M M U N I C A T I O N D E S I G N, A N I M A T E D I M A G E 2014/2015 Lesson #2: Sept. 29 th 2014 Lecture plan: SENSORY AND PERCEPTUAL PROCESSES Basic concepts; Sensation; Perception; Sensation vs. Perception. Extended lesson summary: SENSORY AND PERCEPTUAL PROCESSES B A S I C C O N C E P T S TRANSDUCTION General notion of transduction: - process by which a nervous cell transforms one type of signal in other type of signal. For example: - retina cells transform light energy that enters the eye in electrochemical energy (nervous impulse): Sensation: - transformation in a receptor cell of stimulus energy in neural impulse. EXTENDED SUMMARY OF LESSON #2: - 29 TH SEPT Pag. 1/7

2 CODIFICATION General notion of codification: - process by which a nervous cell translates the physical dimensions of stimulus energy in sensorial dimensions. SENSORIAL DIMENSION CODIFICATION PROCESS Intensity a. Number of receptors activated b. Discharge frequency Quality Type of receptors activated Duration Duration of receptor discharge INTERACTION The reaction of some receptors may be influenced by the reaction of other receptors; Visual system brightness contrast: The color of the two circles are exactly the same although, due to the surrounding color, the circle on the left looks more brownish and the circle on the right looks more reddish. EXTENDED SUMMARY OF LESSON #2: - 29 TH SEPT Pg. 2/7

3 Look at square A and square B. Square A seems to have a darker shade of gray, but, believe it or not, they are exactly the same shade of gray. You can see the proof and get some more information from this illusion in the link: S E N S A T I O N SENSATION AND KNOWLEDGE The importance of knowing our environment; The problem of the origin of knowledge. Two basic assumptions: The empiricists: knowledge origins fundamental from experience of the subject; The innatists: several aspects of our knowledge origin from innate characteristics of human mind (or, as we say nowadays, the brain) THE EMPIRICIST POINT OF VIEW: John LOCKE all our knowledge comes from our senses; Experience: notion of tabula rasa; Knowledge is a copy of external reality: percept equals object. EXTENDED SUMMARY OF LESSON #2: - 29 TH SEPT Pg. 3/7

4 Distal & proximal stimulus: As you can see in the picture above, distal stimulus with different size can produce a proximal stimulus of the same size, as long as the bigger one is farther away from the observer than the smaller one. Sensations: According to empiricist point of view sensation is the basis for the knowledge of the world around us; That knowledge is very important as it can have survival value. For example good notion of motion and depth is important not to have car accidents. The role of association: The organization of our perceptual world depends on past experience; Our past experience consists on the association between sensations; Association may depend on the contiguity of sensations (one sensation is flowed closely by other sensation) Example: Perception of distance: depends on the association by contiguity of the angle of convergence of eye balls and the movement of our arm to reach for something. o Object close to us = wider convergence angle with short arm movement. o Object far from us: = narrow convergence angle with large arm movement. See next image: EXTENDED SUMMARY OF LESSON #2: - 29 TH SEPT Pg. 4/7

5 THE INNATIST POINT OF VIEW Immanuel KANT ( ): Sensations are organized and structured on the basis of certain pre-existent categories (time, space, causality) in our mind. Experience provides the data that is organized accordingly with those categories. Psychophysics Studies the relation between the physical stimulation and the subjective sensations; From stimulus to sensorial experience. Sensorial quality Sensory stimuli = sensory modality? not so... Johannes MÜLLER ( )-doctrine of specific energy of nerves: sensory modalities-depend on nerve structures activated; Various qualities within the same mode: green/red. Sensorial intensity A certain level of sensorial intensity does not correspond to specific psychological intensity; Concepts of: o A Threshold (or limen), is the point of intensity at which the subject can just detect the presence of a stimulus or presence of a difference between two stimuli. Stimuli with intensities below the threshold are considered not detectable (hence: sub-liminal). Stimuli at values close enough to a threshold will often be detectable some proportion of occasions; therefore, a threshold is considered to be the point at which a stimulus, or change in a stimulus, is detected some proportion p of occasions. There are two kinds of thresholds: absolute and difference. o An absolute threshold is the level of intensity of a stimulus at which the subject is able to detect the presence of the stimulus some proportion of the time (a p level of 50% is often used). An example of an absolute threshold is the number of hairs on the back of one's hand that must be touched before it can be felt a participant may be unable to feel a single hair being touched, but may be able to feel two or three as this exceeds the threshold. Absolute threshold is also often referred to as detection threshold. o A difference threshold, or just-noticeable difference (j.n.d.) is the magnitude of the smallest difference between two stimuli of differing intensities that the participant is able to detect some proportion of the time (again, 50% is often used). To test this threshold, several different methods are used. The subject may be asked to adjust one stimulus until it is perceived as the same as the other, may be asked to describe the magnitude of the EXTENDED SUMMARY OF LESSON #2: - 29 TH SEPT Pg. 5/7

6 difference between two stimuli, or may be asked to detect a stimulus against a background. The just-noticeable difference is not a fixed quantity, rather it depends on how intense the stimuli being measured are and the particular sense being measured. Gustav Theodor FECHNER ( ) Fechner's law:-general law relating stimulus intensity and sensory magnitude. S k log I P E R C E P T I O N THE PROBLEM OF PERCEPTION: - HOW DO WE GO FROM THE SENSORIAL TO THE PERCEPTIVE LEVEL? It is important to distinguish the perceptive problem: - when we look to a picture like the next one, what makes that we see an object, in this case an apple, and not just a pattern of colors, light and shadows? In the next picture we see a bushman looking to a Coca-Cola bottle, an object he had never seen he doesn t what it is. This is not a perceptive problem, it is just a cultural problem. He perceives an object but does not identify it. PERCEPTIVE SIGNIFICANCE OF VISUAL INFORMATION: Different issues: EXTENDED SUMMARY OF LESSON #2: - 29 TH SEPT Pg. 6/7

7 o Identification of the nature of the subject = cultural problem; o Construction of the concept of object = psychological (perceptive) problem. Empiricists: experience/memory Innatists: perception depends on organizational factors inherent to perceptual systems. NATURE OF PERCEPTION Perception is: o A proximal and direct process; o A selective process: informational limitation; o An active process: construction of reality; o An hypothetical process: confirmation based on integration within a framework of reference (context); o A relational process: we perceive not only elements but also relations. S E N S A T I O N VS. P E R C E P T I O N Philosophical tradition distinguishes sensation from perception on the basis of complexity: o Sensation is a bodily reaction to an immediate external stimulus or excitement; o Perception is an elaboration on the basis of mental sensations. Sensation leads to perception; According to Gestalt Psychology it is not possible to distinguish sensation from perception. Faro, 9/28/2014 Professor in charge of CU: EXTENDED SUMMARY OF LESSON #2: - 29 TH SEPT Pg. 7/7