Post on 13-Jan-2016
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Chapter 6
Object Perception
Recognition: Relates a current percept to something familiar.
Identification: Recognition of a specific instance.
Categorization: Placing a specific object into a category.
Object recognition
0.1 sec to identify many objects. We typically don’t encounter things
tachistoscopically; but we instead scan. Fixations last typically about .25 sec.
Challenges in object recognition
Occlusion (desk, screen) Upside down Picture of a chair vs. chair Far chair in room vs. toy chair on desk
Two types of theories for object recognition Recognition by components (Biederman) View-based recognition (Bülthoff, Tarr, et
al.)
Geons:
Distinguishable from almost any perspective.
Recognizable even with occlusions.
Pros and cons of geon theory
Explains why it is hard to recognize objects from unusual angles.
No physiological evidence. Sometimes recognition is viewpoint
dependent. Doesn’t explain recognition of individuals.
View-based recognition
People have preferred viewing angles for familiar objects.
Less consensus on preferred viewing angles for novel objects.
Recognition is slower the greater the deviance from preferred viewing angle.
Impact of rotation on recognition
James Stone (1998) showed ameboid images.
Impact of rotation on recognition
James Stone (1998) showed ameboid images.
Guy Wallis (1998) five head shots in apparent rotation.
Learning to see
The young woman – old woman illusion James Elkins experiences with moth
hunting Face - woman illusion High contrast images
Perceptual learning
(p. 203) Panel A: Orientation discrimination Panel B: Vernier acuity (The degree to which a
pair of fine lines can be aligned to each other.) Panel C: Orientation of 3-line bars (followed by
mask) Panel D: Face recognition in the presence of
noise.
Perceptual learning
Chicken sexing Perception of high contrast images (p.
232)Pre-training: 55% for faces; 13% for others.Post-training: 93% for faces; 87% for others.
Inferotemporal cortex
Single cell recording reveals:Few neurons that prefer oriented lines.Neurons with large receptive fields.Neurons that are sensitive to “diagnostic”
features, such as eyes of a face.Neurons that are occlusion insensitive.Neurons that are object size invariant.
Dolan: Viewing gray-scale images facilitates interpreting high contrast versions of those images.
Tovee, Rolls, and Ramachandran, (1996). Monkeys shown black & white, then gray-scale, then black & white again. IT cells were more active the second time around.
Kobatake, Wang, & Tanaka, (1998).
Monkeys shown a target, then after a delay the target with three other objects.
Monkeys improved with practice to be able to perform with longer delays.
IT cells changed firing patterns.
Face Recognition
Much worse when contrast is reversed. Much worse when inverted. The top half of a face is harder to
recognize, when the face is hybridized. Anger is the most distinctive of the six basic
facial expressions (sadness, happiness, anger, fear, surprise, and disgust).
Prosopagnosia
Two types of strategies to cope:Configural: patients base their judgements on
the overall similarity of the faces’ configuration.
Featural processing: patients base their judgements on parts of the face, rather than the whole.
Greebles
http://mail.cog.brown.edu/~tarr/projects/greeble_poster.html
They have symmetric body parts, families, and genders.
Becoming a greeble expert.
Greebles
Expert recognition: As good with general categories as with specific categories.Bird and black-capped chickadeeSex, family, and individual identity
People can become greeble experts after thousands of trials.
Become a Greeble expert
The better a person is at greeble recognition, the more than fMRIs look like facial fMRIs.
The ‘face’ area appears to be deployed in the inspection of even novel greebles.
Attention and object recognition
Attention reduces variability in perception.Prinzmetal, et al., show that distractors
increase trial-to-trial variability in color assessments.
Attention changes an object’s appearance Attention can increase sensitivity of
appearances.
Inattentional Blindness
Spotlight versus object attention
Edgly, Driver, and Rafal (1994)
Moore, Yantis, & Vaughn, (1998), variation
Attention and object recognition
Egly, Driver, and Rafal (1994) suggest that attention is object-based.
The gorilla and girl with umbrella examples also suggest that vision is not a spotlight, but is object-based.
Change Blindness
See demos from Rensink at University of South Dakota.
http://www.psych.ubc.ca/~rensink/flicker/download/
Imagery and Vision
Cheves Perky (1910). Confusability of imagination and vision
fMRI has shown that some of the same brain regions are active during both vision and imagining, including V1. (Kosslyn, et al., 1999)
Imagery and Vision
Cheves Perky (1910). Confusability of imagination and vision
fMRI has shown that some of the same brain regions are active during both vision and imagining, including V1. (Kosslyn, et al., 1999)
TMS to V1 shows that response times on this task are slowed by ~200msec. About the same for both imagery and vision.
What does visual imagery look like? Compare doctored pictures with mental
images. Rate them for similarity on a scale 1-7 when
simultaneously present. Rate them for similarity on a scale 1-7 when
successively present. Images look like vision, except with high
frequency detail removed.
Perceptual Aspects of Reading
Alexia = inability to read acquired late in life.Letter by letter alexia appears to be due to a
visual processing deficit.
The number of saccades and fixation times depends on reading ability and difficulty of material.
Basic facts on reading saccades
Saccades occur on average 0.25 sec. Range of 0.1-0.5 sec. Distance of 2 – 18 letters. 90% of saccades among English readers
are left to right. By making text fill one spot, it is possible
to increase reading rates 3-4 times.
Word superiority effect
Letters can be better recognized in the context of words, than in isolation.
Thus, it appears that words are processed holistically, rather than individually.
Reading through a window
One letter at a time: 90% accuracy on words.
7-9 letters (so entire words could be seen), words were read error-free, but more slowly than normal.
Four words at a time, reading was still slower than normal.
Contextual influences
Expectations shape reading. Unexpected words involve longer fixations.
Spaces in reading
Spaces are not necessary for reading. In fact, you can learn to read about as accurately and with comprehension with as without them.
Fixation points were largely unchanged with the removal of spaces.
Insertion of spaces in the wrong place lead to slowed processing.
Spaces and meaning
Booth, Epelboim, and Steinman (1996). Meaning versus interword spaces.
MeaningfulMeaningless
Normal spacing 100% <<100%
No spacing <100% <<100%
Temporary failures of processing What happens in the face of extreme
ambiguity? Bruner and Potter (1964), studied
perception of defocused images. If you start with more defocused images,
recognition is slowed.Hypothesis: People always conjecture
something and then persevere.
Age and recognition of defocused images Adults are 50% faster than children in
recognition. Adults shape their guesses in a
continuous way; children change their guesses randomly at each stage.