THE STRUCTURE OF THE VISUAL SYSTEM
Questions to Consider:
In what way can striate cortex (V1) be thought of as working like photographic
What was the nature of the first stimulus that Hubel and Wiesel found success
with when conducting single unit recording studies in cats?
How can we use the knowledge that striate cortex has ―line detectors‖ to begin to
develop a theory of object recognition?
Typoglycemia – the human mind does not read every letter by itself, but by the word as
the whole. So letters can be scrambled in a word and as long as the first/last letter are
in place, it can be read.
Does this actually exist?
Why is object recognition important?
Crucial for applying your knowledge
Crucial for learning
o If you couldn’t recognize objects, you couldn’t build knowledge base
How do we perceive and recognize objects?
Form perception: shape and size
Object recognition: identification
Simple visual features Object Recognition Knowledge
There is also a loop where our previous knowledge can help us identify or recognise an
One set of visual features – but two possible interpretations. You can see both but only
one at a time.
Form Perception (cont.) Our perception is not just based on what is actually there to recognise/understand the
Knowledge can change our interpretation
An image can be static but it is our mind that is changing our perception
People resolve ambiguity in everyday situations
Bowl of fruit example: we say that there is one apple behind the banana. It is
ambiguous because it could be two apples but our brain decides no, based on
Principles of Form Perception
Your ability to interpret these scenes is governed by a few basic principles
Similarity: if things are similar, we think them to be part of/the same as one
object. We tend to group similar items together.
Proximity: things that are closer together, we tend to group them with one
Continuity: we think of things as generally continuing, even with something else
Closure: if we can see an entire image as a whole, it doesn’t matter if there are
gaps in that form.
Simplicity: we tend to go for the easiest answer for what would make up an
object With text
Form Perception (cont.)
Brain areas for basic visual features Brain areas for large-scale forms
Context helps with object recognition. We can recognise objects from the front, back,
and even with incomplete information.
Top-Down Influences on Object Recognition
Bottom-up (or data-driven) processing: Stimulus-driven effects Top-down (or concept-driven) processing: Knowledge- or expectation-driven effects
Recognition begins with features—the small elements that result from the organized
perception of form
Commonalities for variable objects
Play a role in visual search
Number of properties in an object can slow you down in identifying it.
Integrative agnosia: Difficulty in judging how more than one feature is bound together in
parietal cortex damage
Disruption of parietal cortex via transcranial magnetic stimulation (TMS)
Methodology for studying word recognition
Words that are familiar are easier to recognise than words that are unfamiliar.
Familiarity: how often a word would appear in a huge text. The ones that are
more frequent are probably more familiar.
Priming: if we’ve previously seen the word, we are more likely to recognize it.