AS Psychology Activity 4

Transcription

1 AS Psychology Activity 4

2 Anatomy of The Eye Light enters the eye and is brought into focus by the cornea and the lens. The fovea is the focal point it is a small depression in the retina, at the back of the eye. The image striking the retina contains vastly more information than is actually transmitted to the brain by the optic nerve.

3 Layers of The Retina Light passes through ganglion cells, then bipolar cells, before reaching the photoreceptor cells (rods and cones) at the back of the retina. Photoreceptors then convert light signals into electrical nerve impulses that are sent to many other retina cells types for processing.

4 The Fovea The ganglion cells at the front of the retina are the final relay station in the eye, and they pass signals into the brain via the optic nerve. The ganglion and bipolar layers thin out at the fovea, allowing light to fall directly onto the photoreceptor cells.

5 The Visual Pathway I The splits and crosses in the first parts of the visual system ensure that the left half of the brain receives information about the right half of the world (here, the spoon handle), and the right half of the brain receives information about the left half of the world (the spoon tip).

6 The Visual Pathway II A small group of fibres in the optic nerve splits off and travels down to groups of brainstem cells control autonomic reflex actions, such as adjusting the size of the pupil, blinking, and eye movement coordination.

7 The Visual Pathway III The majority of fibres in the optic nerve travel to an area of the occipital lobe (at the back of the brain) named the primary visual cortex, or V1. You may wish to briefly describe here the roles of the thalamus and the lateral geniculate nucleus (LGN).

8 The Visual Pathway IV V1 is responsible for creating the basis of a 3-D map of visual space, and extracting features about the form and orientation of objects. Visual information is then sent to the secondary visual cortex, V2, which surrounds V1, for colour and form perception.

9 The Visual Pathway V Most of what we consider to be visual perception occurs in V2 and the higher cortical areas - the extrastriate system. Together, through simultaneous activity, these cortical centers allow us to very quickly see, understand, and respond to an enormous range of visual scenes.

10 Full Moon Illusion Describe the full moon illusion to your classmates. Can they suggest why it occurs? If not, you can enlighten them!

11 Illusions Optical illusions Geometric illusions Artistic optical illusions

12 Optical Illusions To compensate for the loss of information at the retinal level and provide us with visual perceptions that are rich in contrast, colour, and movement, the brain introduces abstract parameters that often fill in or amplify the fragments of reality that it is given to work with. The brain's powers to interpret visual information in this way are so great that it sometimes creates an impression of coherence where there is none - in other words, an optical illusion. The Brain From Top To Bottom, McGill University. Website accessed 05/02/09.

13 Effects of Perspective Lines suggestive of perspective can also create size illusions. Lines that converge towards the horizon are indicators of distance. The effective of perspective (right) is reinforced by the checkerboard pattern, which your brain uses to estimate the size of the two blue vertical lines. The two lines are the same height.

14 Retinal Illusions Whilst most optical illusions result from processes in the occipital cortex, some originate in the retina. The Bird In A Cage Illusion describe it to your classmates works because of its effects on retinal cones. What is happening in the eye? Talk about green cone desensitisation and the residual image.

15 Influences on Perception Context - effects of the objects surrounding Lighting - light sources and three-dimensionality Contours - figure-ground illusions Checkershadow illusion - try explaining the illusion to the right

16 Factors Important in Depth Perception This is more advanced and you may wish to omit this from your presentation. Monocular/binocular vision Interposition Atmospheric perspective Texture gradients Object size Parallax movement Linear perspective

17 Movement Illusions & Receptor Fatigue Describe and show the illusion to the right. Why does this illusion occur? Talk through the waterfall analogy and activation of movement cells in the visual cortex. Then introduce the notion of receptor fatigue and compensation by other receptors involved in movement processing.

18 The illusion that some of the wheels are turning occurs only in your peripheral vision: as soon as you look straight at one of the wheels, it holds still, but the wheels that are peripheral to it keep turning. Source: Akiyoshi Kitaoka, Department of Psychology, Ritsumeikan University, Kyoto, Japan

19 This illusion has not been fully explained, however, a decisive factor in its effect on visual processing is the order in which the four areas of differing colour and brightness are placed. Source: Akiyoshi Kitaoka, Department of Psychology, Ritsumeikan University, Kyoto, Japan

20 Colour Illusions The Hermann grid (right) describe the illusion to your classmates occurs because of a phenomenon named lateral retinal inhibition. How does this work?

21 Angle Illusions State that illusions such as that to the right, feature intersecting lines of the same size, which appear to be of different lengths depending on the angle. Mention that these kind of illusions are difficult to explain at the moment.

22 Form Illusions The traditional description of this illusion s effects: Whilst this image of Lincoln's face looks normal when viewed upside down, when righted it is clearly distorted. As our brains recognise a face only when it is right side up. when it is presented upside down, the brain no longer recognises it as a face but rather as an object. This explains why we do not respond to its distortions. Does this explanation seem acceptable? Do you agree with it? If not, is there a preferable explanation?

23 Conclusions Conclude your talk with three summary points which sum up the content. The study of vision and visual processing is a complex and often abstract area. Well done for completing this activity!