| Why is object perception hard & hard to replicate using computer algorithms? | Stimulus on the retina is ambiguous.
Objects can be hidden (occluded) or blurred.
Objects look different from different viewpoints and in different poses. |
| What are the theories for why humans can successfully perceive objects and scenes? | Structualism.
Gestaltism. |
| Who proposed structualism? | Edward Titchener based on his studies under Wilhelm Wundt. |
| What is structualism? | Distinguishes between:
Sensations - elementary processes occurring in response to stimulation.
Perceptions - conscious awareness of objects and scenes.
Proposed that sensations combine(/sum) to form perceptions. Therefore perceptions contain nothing that was not already present in these elementary sensations. |
| What is Gestaltism? | Claims that conscious awareness is more than the sum of the elementary sensations.
Conscious awareness can therefore have characteristics not present in any of the elementary sensations.
Directly contradicts Structualism. |
| What are the key pieces of evidence for Gestaltism? | Apparent motion.
Illusory Contours. |
| What is apparent motion? | When stationary objects are flashed in succession and perceived to be in motion by the observer.
Therefore the conscious awareness has a character (i.e. motion) not present in the elementary sensations. |
| What are illusory contours? | Visual illusions provoke the perception of an edge/contours (of an image) where there are no physical contours at these locations. |
| According to Gestaltism, humans are able to perceive objects and scenes because of what? | Perceptual organisation (organising a visual image into constituent objects). |
| How is perceptual organisation achieved? | Process of grouping and segregation. |
| What is grouping? | Process by which parts of an image are perceptually bound together to form a perceptual whole (e.g. perception of an object). |
| What is segregation? | Process by which parts of a scene are perceptually separated to form separate wholes (e.g. the perception of separate objects). |
| What are the 5 original Gestalt principles of grouping? | Good continuation.
Pragnanz.
Similarity.
Proximity.
Common fate. |
| What are the two additional Gestalt principles of grouping? | Common region.
Uniform connectedness. |
| What is good continuation? | When aligned (or nearly aligned) contours are grouped together to form a single object.
E.g. in image, A is grouped with B, and C with D. |
| What is Pragnanz? | Groupings occur to make the resultant figure as simple as possible.
Also known as the "principle of good figure or simplicity". |
| What is similarity (in grouping)? | The more similar objects are, the more likely they will be grouped together. |
| Describe how the theory of similarity helps group these objects: | In (a), all the dots are the same colour so it is unclear whether they are organised vertically or horizontally.
In (b), colour similarity groups the dots into columns. |
| What is proximity (in grouping)? Use the image as an example to describe: | The closer the dots are, the more likely they are to be grouped together.
In (a) the dots are equidistant so it is unclear how they are grouped.
In (b), grouping by proximity forms horizontal rows. |
| What is common fate (in grouping)? | Things that are moving in the same way are grouped together. |
| What is common region (in grouping)? | Elements that are within the same region of space tend to group together (Palmer, 1992). |
| What is uniform connectedness (in grouping)? | Connected regions with the same visual characteristics (e.g. colour tend to group together (Palmer & Rock, 1994). |
| What is figure-ground segregation? | The process by which the visual system identifies objects as figures and segregates them from the background. |
| What are figural properties? | They are in front of the rest of the image.
They are at the bottom of the image.
They are convex.
They are recognisable. |
| What is the Rubin vase an example of? | Figural properties.
Demonstrates that depth ordering affects figure perception (regions of an image in front of the image tend to be seen as figures/objects). |
| Explain the trend between the images and the graph in terms of segregation: | Lower is seen as the figure due to figural properties.
There is no left/right bias which is why (b) is around 50%. |
| What is gist perception? | When not all objects in a scene are identified (e.g. due to lack of time), but the subject can get an overall impression of what the scene is about. |
| What did Potter (1976) study and find? | Gist perception.
Subjects were shown 16 randomly chosen scenes for 250 ms each and were asked if any of the scenes fitted the description.
Observers near 100% accuracy.
Therefore observers can rapidly perceive a scene's gist. |
| What did Fei-Fei investigate and find? | Investigated minimum scene exposure time is needed to perceive a scene's gist.
Longer the stimulus presentation time, more detailed and accurate the description.
Observers could start to perceive aspects of the scene at about 27ms but perceptions were not very detailed.
Very accurate perception achieved in 250ms. |
