A visual imagery task is presented which is beyond the limits of normal human ability, and some of the factors contributing to its difficulty are isolated by comparing the difficulty of related tasks. It is argued that complex objects are assigned hierarchical structural descriptions by being parsed into parts, each of which has its own local system of significant directions. Two quite different schemas for a wire‐frame cube are used to illustrate this theory, and some striking perceptual differences to which (...) they give rise are described. The difficulty of certain mental imagery tasks is shown to depend on which of the alternative structural descriptions of an object is used, and this is interpreted as evidence that structural descriptions are an important component of mental images. Finally, it is argued that analog transformations like mental folding involve changing the values of continuous variables in a structural description. (shrink)

This paper describes a computer simulation of reading that is strongly driven by eye fixation data from human readers. The simulation, READER, is a natural language understanding system that reads a text word by word and whose processing cycles on each word have some correspondence with the human gaze duration on that word. READER operates within a newly developed information processing architecture, a Collaborative, Activation‐based, Production System (CAPS) that permits the modeling of the temporal properties of human comprehension. CAPS allows (...) for concurrent, collaborative execution of processes operating at different levels of analysis. As READER encounters each successive word, the word is operated on by processes at the levels of word encoding, lexical access, syntactic and semantic analysis, and referential and schema‐level processes. Like human readers, READER uses a strategy of immediacy of comprehension, attempting to interpret each word as soon as it is encountered, rather than unnecessarily buffering information. A major contribution of this simulation is its use of human performance characteristics in constraining and determining the model's mechanisms. (shrink)