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 eeble_poster.html eeble_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 chickadee  Sex, 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. ownload/ ownload/

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 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 spacing100%<<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.