PNB 2XA3 Lecture Notes - Lecture 7: Necker Cube, Template Matching, Tim Hortons
23 Sep 2018
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Lecture 7 – Tuesday September 18
• Visual illusions often occur because one’s interpretation of the stimulus is incorrect
• Bottom up processing: taking sensory info and then assembling and integrating it
o Data driven
o Requires stimulus
o What am I seeing?
• Top down processing: using models, idea, and expectations to interpret sensory information
o Conceptual driven
o Prior expectations
▪ Ex. culture, belief, prejudice, goal, presence of authority, knowledge,, vocab, life
experience, mood, memory, mental health
• Paradolia – being able to see dog/ faces in art
o Jesus Christ appeared on the side of a Tim Horton’s building
• Top down processing
o We see a cube when its just circles with lines in them
o We have seen the necker cube before so we perceive the cube immediately
• B and 13 is neutral and ambiguous stimulus
o We added a line in between so we assumed that there are continuous lines and we now
better perceive it as B
• We have no top down expectations with the scap piees of paper
o By adding the occlude (filling the white space) we now perceive the B’s
• Object recognition – once the form has been organized by our perceptual system (ex. what parts
belng together, ewhat is figure and what is ground), we then identify the object
o How do we build internal represetnations of objects during the process of identification
▪ Object recognition does not equal object perception
• Contextual effects
o THE CAT (H and A are the same but we can still read the similar A as H due to top down
processing)
o Ambiguous at the feature and letter levels; disambiguated at the world level
o There is much more here than perception. How do we go from object perception to
recognition ? There needs to be contact between the emerging percept and meory
• It doesn’t matter in what order the letters in a word are, the only important thin is that the first
and last letter be at the right place. The rest can be a total mess and you can still read it without a
problem. This is because the human mind does not read every letter by iteselvf, but the word as a
whole
o Illustrate top down processing – we fill in omissions and mistkes on the basis of our
experience and expectations
• What happens when the pattern recognition system is damaged?
o Object agnosia (unable to recognize objects)
▪ Ex. the man who mistook his wife for a hat. When in the street, he might pat the
heads of water-hydrants and parking meteres, taking these to be the heads of
children; he would amiably addres varved knobs on the furniture, and be
astounded when they did not reply
▪ Apperceptive agnosia (perceptual representation)
➔ Cannot recognize by shape
➔ Cannot copy drawings
