Categorizations which humans make of the concrete world are not arbitrary but highly determined. In taxonomies of concrete objects, there is one level of abstraction at which the most basic category cuts are made. Basic categories are those which carry the most information, possess the highest category cue validity, and are, thus, the most differentiated from one another. The four experiments of Part I define basic objects by demonstrating that in taxonomies of common concrete nouns in English based on class inclusion, basic objects are the most inclusive categories whose members: (a) possess significant numbers of attributes in common, (b) have motor programs which are similar to one another, (c) have similar shapes, and (d) can be identified from averaged shapes of members of the class. The eight experiments of Part II explore implications of the structure of categories. Basic objects are shown to be the most inclusive categories for which a concrete image of the category as a whole can be formed, to be the first categorizations made during perception of the environment, to be the earliest categories sorted and earliest named by children, and to be the categories

In this article we present a standardized set of 260 pictures for use in experiments investigating differences and similarities in the processing of pictures and words. The pictures are black-and-white line drawings executed according to a set of rules that provide consistency of pictorial representation. The pictures have been standardized on four variables of central relevance to memory and cognitive processing: name agreement, image agreement, familiarity, and visual complexity. The intercorrelations among the four measures were low, suggesting that the) ' are indices of different attributes of the pictures. The concepts were selected to provide exemplars from several widely studied semantic categories. Sources of naming variance, and mean familiarity and complexity of the exemplars, differed significantly across the set of categories investigated. The potential significance of each of the normative variables to a number of semantic and episodic memory tasks is discussed. Investigators studying aspects of verbal processes have long had access to extensive normative data on various objective and subjective dimensions of their verbal materials. Brown (1976) recently compiled a catalog of scaled verbal materials that included 172 studies providing such information. For the set of verbal materials most comparable to the present set of pictures—English nouns—such dimensions include objective measures of frequency of occurrence and subjective measures of familiarity, age of acquisition, concreteness, imagery, meaningfulness, and emotionality. In contrast, normative data on characteristics of pictorial representations of concrete

In this paper we propose and evaluate new graphical password schemes that exploit features of graphical input displays to achieve better security than textbased passwords. Graphical input devices enable the user to decouple the position of inputs from the temporal order in which those inputs occur, and we show that this decoupling can be used to generate password schemes with substantially larger (memorable) password spaces. In order to evaluate the security of one of our schemes, we devise a novel way to capture a subset of the "memorable" passwords that, we believe, is itself a contribution. In this work we are primarily motivated by devices such as personal digital assistants (PDAs) that offer graphical input capabilities via a stylus, and we describe our prototype implementation of one of our password schemes on such a PDA, namely the Palm Pilot.

The fan effect (Anderson, 1974) has been attributed to interference among competing associations to a concept. Recently, it has been suggested that such effects might be due to multiple mental models (Radvansky, Spieler, & Zacks, 1993) or suppression of concepts (Anderson & Spellman, 1995; Conway & Engle, 1994). We show that the ACT-R (Adaptive Control of Thought-Rational) theory, which embodies associative interference, is consistent with the Radvansky et al results and we fail to find any evidence for concept suppression in a new fan experiment. The ACT-R model provides good quantitative fits to the results from a variety of experiments. The three key concepts in these fits are (a) the associative strength between two concepts reflect the degree to which one concept predicts the other; (b) foils are rejected by retrieving mismatching facts; and (c) subjects can adjust the relative weights they give to various cues in retrieval.

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This special issue is devoted to recent work on mental imagery. To get a sense for the subject matter, answer the following questions: How many windows are there in your living room? What socks did you wear yesterday? Is there room in your refrigerator for a litre of milk? These questions typically evoke visual mental imagery. For example, when answering the first, people usually visualize the room, and then 'scan ' over each wall, 'seeing ' each window with their mind's eye. Similarly, if asked whether a cat's meow has a higher pitch than the sound of a blender, most people report 'hearing ' the sounds in their 'mind's ear'. Such tasks evoke auditory mental imagery. Visual mental imagery is 'seeing ' in the absence of the appropriate immediate sensory input, auditory mental imagery is 'hearing ' in the absence of the appropriate immediate sensory input, and so on. Imagery is distinct from perception, which is the registration of physically present stimuli. The examples illustrate that imagery plays an important role in memory and spatial reasoning, but as we shall see, these functions merely scratch the surface. Imagery also plays a role in abstract reasoning, skill learning, and language comprehension.

Can theories of mental imagery, conscious mental contents, developed within cognitive science throw light on the obscure (but culturally very significant) concept of imagination? Three extant views of mental imagery are considered: quasi-pictorial, description, and perceptual activity theories. The first two face serious theoretical and empirical difficulties. The third is (for historically contingent reasons) little known, theoretically underdeveloped, and empirically untried, but has real explanatory potential. It rejects the “traditional ” symbolic computational view of mental contents, but is compatible with recent situated cognition and active vision approaches in robotics. This theory is developed and elucidated. Three related key aspects of imagination (non-discursiveness, creativity, and seeing as) raise difficulties for the other theories. Perceptual activity theory presents imagery as non-discursive and relates it closely to seeing as. It is thus well placed to be the basis for a general theory of imagination and its role in creative thought.

Two experiments are reported in which Ss were required to determine whether a random, angular form, presented at any of a number of picture-plane orientations, was a “standard ” or “reflected ” version. Average time required to make this determination increased linearly with the angular departure of the form from a previously learned orientation. The slope and intercept of the reaction-time (RT) function were virtually constant, regardless of the perceptual complexity of the test form and the orientation selected for initial learning. When Ss were informed in advance as to the identity and the orientation of the upcoming test form and, further, were permitted to indicate when they were prepared for its external presentation, RT for determining the version of the form was constant for all test-form orientations. However, the time needed to prepare for the test-form presentation increased linearly with the angular departure of the form from the learned orientation. It is argued that the processes both of preparing for and of responding to a disoriented test form consist of the mental rotation of an image, and that both sorts of mental rotation (pre-stimulus and post-stimulus) are carried out at essentially the same constant rate. During the past several years, experimental and theoretical investigation of nonverbal internal representation, particularly mental imagery, has proliferated. The primary focus of this renewed experimental effort has been directed toward questions concerning the functional significance of mental imagery (e.g., Bower, 1972; Paivio, 1971). With the exception of evidence concerning the modality or the coded form of internal representations- deriving primarily from the “selective interference”

A central concern of psycholinguistic research is explaining the relative ease or difficulty involved in processing words. In this thesis, we explore the connection between lexical processing effort and measurable properties of the linguistic environment. Distributional information (information about a word's contexts of use) is easily extracted from large language corpora in the form of co-occurrence statistics. We claim that such simple distributional statistics can form the basis of a parsimonious model of lexical processing effort.