Perceptual Object Recognition (Lecture 6) Flashcards
What is a perceptual object-file?
Treisman’s leading theory proposes internal representations called “object-files”- object files= used to store features of objects that are being attended to; integrated with prior knowledge.
Support out ability to attend to objects as they undergo change and occlusion over time (Kahneman & Treisman, 84):
- occlusion: blocked, obstructed, covered, obscured.
Thought to be the end-product of perceptual binding processes according to FIT.
Why do we need object files?
Psychologists traditionally appeal to two types of visual representation:
- early low level perceptual features (eg. it’s red)- perceiving = knowing the features.
- later higher level recognised objects (eg. its an apple).
However this does not explain many aspects of visual processing.
- found objects can be perceivable while unidentifiable (K, T & Gibbs, 92)- need a mid level representation= object files.
What are object files for?
Mid level representations that maintain object continuity despite movement and partial occlusion/obscuring.
Help mediate out conscious perception of persisting objects.
Tell us which went where.
Flexible: allow us to represent novel objects which we have no pre-existing knowledge.
They allow us to represent multiple identical object (segregated on the grounds of location and spatiotemporal continuity).
How do perceptual object files work?
Perception matches an existing object-file: that file is retrieved.
Mismatch between perception and existing file: the file is updated.
Serious mismatch between perception and existing file: a new file is created (and a new object perceived).
Object files allow the tracking of moving objects.
Object files and spatial location: reviewing paradigm (K, T, G, 92)
Stimuli: two successive displayed each containing boxes.
- first display contains two or more letter in boxes while the second only contains a single letter in a box.
- letter can either match the letter from that box in initial display, from a different box, or entirely new letter.
Task= name the single letter.
Found: RTs faster when the letter was repeated between preview and probe (general priming).
- but RTs still faster when the probe letter matched both the identity and location of one of the preview letters.
Interpretation: when viewing the preview display, OFs were created containing letter info (tied to location).
- If probe matched both features (letter and location) the file was retrieved.
- If there was a partial match (letter moved box) the file was updated.
- If there was no match, new object-file needed to be created.
Object files and motion: K, T, G, 92
Found: faster to name letter when it was in the same object/frame compared to different object files and no match.
Interpretation: the object files were tracked to their new locations- an object-specific preview effect was experienced.
Multiple object tracking (MOT) task: overview
Plyshyn and colleagues: explored the processes that track attended objects through movement- many key findings on object tracking have emerged from the use of this paradigm.
Ppts asked to indicate whether a highlighted individual is part of the attended set or not.
Scholl (2001)- found ppts can accurately track around 3 items- amount of object files that can be tracked is severely limited, much like our attentional capacity.
Tracking objects in the face of uncertainty- spatio-temporal continuity is critical
Feature changes do not open a new object file: Scholl, Pylyshyn and Frannceroni (1999):
Once claim of these mid level representations is their ability to track objects despite uncertainty about objet identity.
This has also been measure in the MOT task.
Used adapted version of MOT task to study object-file tracking during uncertainty about object identity?- same as MOT task except targets and distracters change colour during motion.
- typical finding: changing colours of the tracked objects has little, if any, impact on tracking performance.
Scholl & Pylyshyn, 1999: found occlusion (obstruction varying how easy it was to see them) did not damage performance.
- however, when disappearance was not spatio-temporally consistent performance was damaged.
In order for objects to be tracked, they must maintain a spatio- temporally plausible path of motion, even if change occurs.
Object files are sticky, but motion must be consistent with reality and expectation.
Summary
Object-files are set up on the basis of integrating features via spatial attention paid to their share spatial position.
Spatial info is important once object files are set up.
When objects move, spatiotemporal continuity is critical- studies have used MOT task; S & P, 99- object file tracking can survive change so long as motion is plausible.
