Lance J. Rips

Similarity, typicality, and categorization

Here is a simple and appealing idea about the way people decide whether an object belongs to a category: The object is a member of the category if it is sufficiently similar to known category members. To put this in more cognitive terms, if you want to know whether an object is a category member, start with a representation of the object and a representation of the potential category. Then determine the similarity of the object representation to the category representation. If this similarity value is high enough, then the object belongs to the category; otherwise, it does not. For example, suppose you come across a white three-dimensional object with an elliptical profile; or suppose you read or hear a description like the one I just gave you. You can calculate a measure of the similarity between your mental representation of this object and your prior representation of categories it might fit into. Depending on the outcome of this calculation, you might decide that similarity warrants calling the object an egg, perhaps, or a turnip or a Christmas ornament. This simple picture of categorizing seems intuitively right, especially in the context of pattern recognition. A specific egg – one you have never seen before – looks a lot like other eggs. It certainly looks more like eggs than it looks like members of most other categories. And so it is hard to escape the conclusion that something about this resemblance makes it an egg or, at least, makes us think its one.

Combining prototypes: A selective modification model

Abstract We propose a model that accounts for how people construct prototypes for composite concepts out of prototypes for simple concepts. The first component of the model is a prototype representation for simple, noun concepts, such as fruit, which specifies: (1) the relevant attributes of the concepts, (2) the possible values of each attribute, (3) the salience of each value, and (4) the diagnosticity of each attribute. The second component of the model specifies procedures for modifying simple prototypes so that they represent new, composite concepts. The procedure for adjectival modification, as when red modifies fruit, consists of selecting the relevant attribute(s) in the noun concept (color), boosting the diagnosticity of that attribute, and increasing the salience of the value named by the adjective (red). The procedure for adverbial modification, as in very red fruit, consists of multiplication-by-o-scalar of the salience of the relevant value (red). The outcome of these procedures is a new prototype representation. The third component of the model is Tverskys (1977) contrast rule for determining the similarity between a representation for a prototype and one for an instance. The model is shown to be consistent with previous findings about prototypes in general, as well as with specific findings about typicality judgments for adjective-noun conjunctions. Four new experiments provide further detailed support for the model.

The Subjective Dates of Natural Events in Very-Long-Term Memory

This research explores the problem of how people determine the time of public events, such as the attempted assassination of Ronald Reagan or the Three-Mile Island accident. According to what here is called the accessibility principle, the subjective dates of these events depend in part on the amount that can be recalled about them: The more known, the more recent the event will seem. Experiments 1 and 2 demonstrate this effect when subjects estimate explicit dates for important news stories of the 1970s and 1980s. The same effect appears in Experiment 3 for subjects who rate the recency of less known events drawn from a single week. Accessibility also contributes to the amount of time needed to compare the subjective date of an event (e.g., the Jonestown suicides) to an explicitly presented date (e.g., November 1979), as shown in Experiment 4. The accessibility principle for time estimation can be conceived as one of a related group of retrieval-based inferences that plays a part in judgments of frequency and probability and judgments about the falsity of a putative fact.

Two Kinds of Reasoning

According to one view of reasoning, people can evaluate arguments in at least two qualitatively different ways: in terms of their deductive correctness and in terms of their inductive strength. According to a second view, assessments of both correctness and strength are a function of an arguments position on a single psychological continuum (e.g., subjective conditional probability). A deductively correct argument is one with the maximum value on this continuum; a strong argument is one with a high value. The present experiment tested these theories by asking participants to evaluate the same set of arguments for correctness and strength. The results produced an interaction between type of argument and instructions: In some conditions, participants judged one argument deductively correct more often than a second, but judged the second argument inductively strong more often than the first. This finding supports the view that people have distinct ways to evaluate arguments.

Psychological connectedness and intertemporal choice

People tend to attach less value to a good if they know a delay will occur before they obtain it. For example, people value receiving

From numerical concepts to concepts of number

100 tomorrow more than receiving

Interpreting and evaluating metaphors

100 in 10 years. We explored one reason for this tendency (due to Parfit, 1984): In terms of psychological properties, such as beliefs, values, and goals, the decision maker is more closely linked to the person (his or her future self) receiving

Similarity as an explanatory construct

100 tomorrow than to the person receiving

Necessity and Natural Categories

100 in 10 years. For this reason, he or she prefers his or her nearer self to have the

Categories and resemblance.

100 rather than his or her more remote self. Studies 1 and 2 showed that the greater the rated psychological connection between 2 parts of a participants life, the less he or she discounted future monetary and nonmonetary benefits (e.g., good days at work) over that interval. In Studies 3-5, participants read about characters who undergo large life-changing (and connectedness-weakening) events at different points in their lives and then made decisions about the timing of benefits on behalf of these characters. All 5 studies revealed a relation between perceived psychological connectedness and intertemporal choice: Participants preferred benefits to occur before large changes in connectedness but preferred costs to occur after these changes.