HUL 211 Orientation in object perception and memory

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					           Orientation
in object perception and memory




          Snehlata Jaswal


          HUL 211 OBJECT PERCEPTION AND MEMORY
HUL 211 OBJECT PERCEPTION AND MEMORY
HUL 211 OBJECT PERCEPTION AND MEMORY
            Why we saw Mona Lisa
Objects, like faces, are stored in their usual orientation: an
object centered representation.

When we see features like the eyes, we re-map what our
eyes see into this representation.

For reasons that are not fully understood, this re-mapping
fails when these features are seen in unusual orientations.

Perhaps it is simply a lack of practice.




                      HUL 211 OBJECT PERCEPTION AND MEMORY
                      Orientation
Perception of the orientation of objects is important in our
  interaction with the environment. It is important for form as
  well as pattern perception.

Three issues:

1. How do we perceive orientation as a feature

2. How does perception of orientation affect the perception of
   objects

3. How do we orient ourselves in relation to objects in the
   environment


                     HUL 211 OBJECT PERCEPTION AND MEMORY
 Perceiving orientation as a feature




Usually the task used presents lines such as the above in
various orientations, with a predefined target to be identified as
quickly as possible, or the change in orientation from one
screen to another to be noticed as soon as possible.
                     HUL 211 OBJECT PERCEPTION AND MEMORY
Perceiving orientation as a feature




To study conjunctions coloured lines may be used



                HUL 211 OBJECT PERCEPTION AND MEMORY
Perceiving orientation as a feature




Gratings, presented in Gabor patches have also been used
  to study perception of orientation in patterns. The question
  here is whether the Gabor is detected or not given the
  frequencies depicted in the Gabor
                    HUL 211 OBJECT PERCEPTION AND MEMORY
Perceiving orientation as a feature
  Some interesting results:

1. Orientation is as important as colour as a feature –
   perhaps slightly more so.

2. Vertical and horizontal orientations are perceived more
   accurately and precisely than oblique ones (the oblique
   effect).

3. Detection thresholds for Gabor patches of different
   orientations and spatial frequencies are strongly related
   to the probabilities that these configurations occur in
   ’natural’ images. Thus the statistical properties of our
   environment ‘guide’ our detection of orientation.

                    HUL 211 OBJECT PERCEPTION AND MEMORY
                Orientation in the brain
In higher areas of the brain, "like" cells like to be near each other. This reduces
the length of the axons and of the wiring in the brain. So cells exist in modules
or columns.

Object perception begins in V1 which extracts simple features that are common
to all images. E.g., if 4 lines form a box, when one sees a box, a number of
orientation specific simple cells in V1 are activated. According to synchrony
theory, when the cells that detect 4 lines fire together, the object is likely to be
perceived as a box. However, no one has as yet explained WHY this occurs.

From V1 information is sent to higher order visual areas, first V2 and then to
V3. From V3 information diverges to over 3 dozen higher order visual areas.
Each processes some special aspect of visual information.

In these higher order visual areas the brain begins assembling simple features
into objects. It is here that the visual system starts to assemble lines and edges
into objects.


                            HUL 211 OBJECT PERCEPTION AND MEMORY
HUL 211 OBJECT PERCEPTION AND MEMORY
        Object perception in the cortex
In the higher order visual areas the brain assembles simple features into
objects.
• In the ventral stream object perception area, the Lateral Occipital Complex
  (LOC), object parts in the upper and lower visual fields are brought together
  again (but not left and right).
• Areas in the inferior temporal cortex code whole objects. Cells respond
  selectively to a particular class of object, e.g. faces, hands, animals etc. Cells
  that respond to the shape of hands do not respond to faces. Cells are tuned
  to particular instances of object, e.g. a particular animal. The response of
  these cells is the same independent of
     i) the location of the object’s image on the retina
     ii) the size of the image
     iii) the cue the defines the objects shape (e.g. lines, color, texture, motion).
• An important part of the inferior temporal cortex is the FFA, specialized to
  code faces. Small lesions in the Fusiform face area in the inferior temporal
  cortex produce prosopagnosia, a specific loss of face recognition. Such
  patients cannot recognize faces of friends, though they can recognize them
  through their voice.

                             HUL 211 OBJECT PERCEPTION AND MEMORY
Development of perception of orientation
McGurk (1970)

Experiment 1:
- Used the spontaneous visual preference procedure,
- 6-26 mth old babies were exposed to pairs of objects in different orientations
- failed to show discrimination between orientations.

Experiments 2 and 3:
Babies were firstly habituated to the appearance of objects in a constant
orientation before being presented with the same objects in another
orientation.
Results showed:
(a) that infants between 6 and 26 weeks perceive the change that occurs
    when the orientation of an object is altered by 180 deg.
(b) they perceive the difference between an otherwise identical pair of
    relatively simple abstract shapes when their orientations differ by 180 deg.
(c) with facial objects it was only subjects in the 20 to 26 weeks age range
    who appeared to make this latter discrimination.
                           HUL 211 OBJECT PERCEPTION AND MEMORY
               Orientation in space
Dobbins and Grossman (2010): An experiment with the Necker cube




                       HUL 211 OBJECT PERCEPTION AND MEMORY
How stable is the bias?




     HUL 211 OBJECT PERCEPTION AND MEMORY
                                Results
People have a preference for seeing ambiguously oriented
objects (Necker cubes) as if tilted down or viewed from above.

This bias is a near certainty in the first instance (1 s) of viewing
and declines over the course of many seconds.

There is modulation of perceived orientation that varies with
position—for example objects on the left are more likely to be
interpreted as viewed from the right.

These results are consistent with the idea that ambiguously
oriented objects are initially assigned an orientation consistent
with our experience of an asymmetric world in which most
objects are illuminated from above and are placed below eye
level.
                        HUL 211 OBJECT PERCEPTION AND MEMORY
  An experiment with mirror images
Gregory and McCloskey (2010)

Stimuli were real life objects presented in various orientations

Asked their subjects to actually draw the images in response
to two stimuli presented on screen for 500 ms each followed
by a mask

Interestingly, the objects were presented not only vertically or
horizontally, but rotated in various ways.




                     HUL 211 OBJECT PERCEPTION AND MEMORY
          Why we saw Mona Lisa
Objects




              HUL 211 OBJECT PERCEPTION AND MEMORY
Target stimuli in various orientations




           HUL 211 OBJECT PERCEPTION AND MEMORY
           Possible errors

                          OPA Object Principal Axis reflection
                          OSA Object Secondary Axis reflection
                          EVA Extrinsic Vertical Axis reflection
                          EHA Extrinsic Horizontal Axis reflection




HUL 211 OBJECT PERCEPTION AND MEMORY
HUL 211 OBJECT PERCEPTION AND MEMORY
         Thank you




HUL 211 OBJECT PERCEPTION AND MEMORY

				
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Description: Object Perception and Memory Lecture Series