1. Recognizing Visual and Auditory Stimuli
Assist. Prof. Dr. Ilmiye Seçer
Fall

2. Recognizing Visual and Auditory Stimuli
Background on visual object recognition
Top-down processing and visual object recognition
Face perception
Speech perception

3. Recognizing Visual and Auditory Stimuli
What is Perception?
Perception uses previous knowledge to gather and interpret the stimuli registered by the senses.
Being able to read these slides is due to perception.
You combined information registered by your eyes, your previous knowledge about the shape of the letters, and your previous knowledge about what your visual system has already registered (i.e., perceptio-).

4. Recognizing Visual and Auditory Stimuli
What is object or pattern recognition?
The identification of sensory stimuli is perceived to be separate from its background.

5. Background on Visual Object Recognition
Two terms to refer to perceptual stimuli:
Distal Stimulus
Actual object in the environment
Proximal Stimulus
The information registered on your sensory receptors – i.e., the image that your phone creates on your retina.
Retina – back portion of your eye that contains millions of neurons that register and transmit visual information from the environment.

6. Background on Visual Object Recognition

7. Background on Visual Object Recognition
An object is recognized when we figure out what the distal stimulus is even if the information from the proximal stimulus is not perfect.
For example, you recognized the face (previous slide) even when the nose was missing.

8. Background on Visual Object Recognition
An object can be recognized in one-tenth of a second.
Visual system gains assistance from other brain regions, such as, iconic memory or visual sensory memory.
An image of a visual stimulus is held here for a brief period of time after the stimulus has disappeared.

9. Background on Visual Object Recognition
Visual information registered on the retina travels via neurons to the visual cortex.
The primary visual cortex is located in the occipital lobe (at the back of the brain) and processes basic visual stimuli after combining information received from both eyes.

10. Organization in Visual Perception
Gestalt Psychology
Humans organize what they see.
Without effort we see patterns rather than random arrangements.

11. Organization in Visual Perception

12. Organization in Visual Perception

13. Organization in Visual Perception

14. Organization in Visual Perception
Gestalt Psychology
The figure has a distinct shape with clearly defined edges, while the ground forms the backgroundnd.

15. Organization in Visual Perception

16. Organization in Visual Perception
What about times when the figure becomes the ground and the ground becomes the figure?
Ambiguous figure-ground relationship

17. Organization in Visual Perception

18. Organization in Visual Perception

19. Organization in Visual Perception

20. Organization in Visual Perception
Human perception is more than the information present in the distal stimulus.
What could be the reason why we alternative between figures in the previous two pictures?

21. Theories of Visual Object Recognition
Feature Analysis Theory
Visual stimulus is composed of small components called distinctive features.
How do we recognize letters of the alphabet?
We store a list of distinctive features for each letter.
For example, the letter R has a curved feature and a vertical and diagonal line.
The visual systems considers these presence or absence of features and compares it to the information stored in memory to detect the letter it has seen.

22. Theories of Visual Object Recognition
The Recognition by Components Theory
Explains how we recognize 3D shapes.
Objects are made up of shapes called geons.
Geons are combined to make up different meaningful objects.
Modification to this theory is needed since we sometimes recognize objects faster when they are in the usual view.

23. Theories of Visual Object Recognition

24. Theories of Visual Object Recognition
Viewer-Centered Approach (Modification)
We store a number of views of 3D objects rather than just one view.
When we see a view of an object that is unusual and not stored in memory, it may take longer for us to recognize it. This is because we mentally rotate the object until it fits the image we have stored in memory.
And sometimes we don't recognize the object at all.

25. Theories of Visual Object Recognition

26. Top Down Processing and Visual Object Recognition
Does our knowledge and expectations aid recognition?

27. Top Down Processing and Visual Object Recognition
Bottom up processing
Stimulus characteristics are important to recognize an object
E.g., shape, size, color
Once physical characteristics are perceived, higher order processes begin to help recognize the object

28. Top Down Processing and Visual Object Recognition
Person’s concepts, expectations, and memory influence object recognition.
Top down processing is important when the object has been presented briefly or is incomplete or ambiguous.

29. Bottom Up and Top Down Processing

30. Bottom Up and Top Down Processing

31. Bottom Up and Top Down Processing

32. Top Down Processing and Reading

33. Top Down Processing and Reading

34. Top Down Processing and Reading
Word Superiority Effect
We can identify a single letter more accurately and more rapidly when it appears in a meaningful word than when it appears alone or in a meaningless string of unrelated letters.
For example, you can recognize the letter p faster and more accurately if it is presented as part of the word palm than if it were presented in a nonword such as mpzs

35. Top Down Processing and Reading
How can you explain the word superiority effect?
The McClelland and Rumelhart Model
Detection of the letter T excites all words with T and inhibits the activation of all words without a T

36. Top Down Processing and Reading

37. Top Down Processing and Reading
The McClelland and Rumelhart Model
The word TRIP is shown
Feature detectors activated
Only letters R, I, & P detecetd
Excite the letter detectors for these letters
Inhibit all other letters
The word detector will then be activated
TRIP provides the context that T is quite likely

38. Top Down Processing and ‘Smart Mistakes’ in Object Recognition
When we overuse top down processing, we:
(a) may fail to detect changes in an object or scene, known as change blindness, or
(b) may not notice an unexpected yet visible object, known as inattentional blindness.
When an object appears that is not consistent with our memory and expectations we may fail to see it.

39. Face Perception
Face recognition is special-we recognize faces on a holistic basis (i.e., in terms of overall shape and structure).
People with prosopagnosia cannot recognize human faces and rather than seeing a complete face, they see a nose, mouth, and two eyes independent of one another.
Face recognition occurs in the temporal lobe.
Read page 55 and 56 on the applications of face perception.

40. Speech Perception
The auditory system needs to record the sound vibrations generated by someone speaking, then these vibrations needs to be translated to sounds that we perceive as speech.
We must also separate the voice of the speaker from the background noise and variety of nonspeech sounds.

41. Speech Perception Characteristics of Speech Perception
Speech sounds are known as phoneme.
Consider the sound of a and t
1. Boundaries between words can be occur even when there is no silence between words (Hearing speech in Turkish versus İtalian)
2. Phoneme pronunciation varies (my Australian English accent versus Ariel Hoca’s American English accent),
3. Context allows listeners to fill in some missing sounds,
4. Visual cues from the speaker’s mouth help us interpret sounds.

42. Speech Perception Theories of Speech Perception
The Special Mechanism Approach
Humans born with innate device to decode speech
Speech decoded better for speech than nonspeech sounds such as instrumental music (i.e., a phonetic module).
The General Mechanism Approach
Speech perception is a learned skill
Same brain regions active during speech and music

43. Chapter 2 Review Questions
1. How would you describe perception to someone who has never taken a course in cognitive psychology? Provide examples of two visual and two auditory cognitive tasks. Use terms that we have covered in this chapter. 2. How would top-down processing operate when you smell a certain fragrance and try to identify it? Then provide an example for both taste and touch.