McKinnon, W., Weisse, C.S., Reynolds, C.P., Bowles, C.A., & Baum, A. (1989). Chronic stress, leukocyte subpopulations, and humoral response to latent viruses. Health Psychology. 8, 389-402. Meyer, R.J., & Haggerty, R.J. (1962). Streptococcal infections in families. Pediatrics. 29, 539549. Rabin, B.S , Cohen, 5., Ganguli, R., I.vie, D.T., & Cunnick, J.E. (1989). Bidirectional interaction between the central nervous system and immune system. CRC Critical Rei'iewb in humunologu, 9, 279-312. Stone, A.A., Bovbjerg, D.ll., Neale, J.M.,

Napoli, A., Valdimarsdottir, H., Cox, D., Hayden, E.G., &Gwaltney, J.M. (1993). Development of common cold symptoms foUowmg expcrmiental rhinovirus infection is related to prior stressful life events Behavioral Medicme, 8, 115-120. Stone, A.A., Cox, D.S., Valdimarsdottir, H., Jandorf, L., & Neale, J.M. (1987). Evidence that secretory igA antibody is a.ssocuited with daily mood, journal of Personality and Social Psychology, 52, 988-993. Stone, A.A., Neale, |.M., Cox, D.S., Napoli, A., Valdimarsdottir, H., & Kennedy-Moore, F (1994). Daily events are associated with ii secre-

Possible Individuals in Language and Cognition Paul Bloom^ Department of Psychology, University of Arizona, Tucson, Arizona

One approach to the psychology of proper names and count nouns explores the role these expressions play in our mental life. Proper names such as fido correspond to entities we think of as individuals—entities that can be categorized, counted, and tracked over space and time. Count nouns such as dog correspond to kinds of individuals. It makes sense to talk of 2 dogs or 10 dogs, or to say that a certain dog is the same one that I saw yesterday, or to ask what happened to Fido. Not all parts of speech refer to individuals; adjectives like hig and mass nouns like water do not correspond to entities that are countable or trackable in the same sense. This observation raises the question of what sorts of entities are naturally thought of as individuals. We count, name, and track dogs—they are psychologically natural individuals. As a result, words that refer to this kind {dog) and words that refer to particular members of this kind {Fido) are easily learned by children. But not every logically possible individual is acceptable from the standpoint of human psychology. For in-

stance, construing the spatially discontinuous entity composed of my dog and his favorite bone as a single individual is cognitively unnatural. We could not easily learn a proper name {Fidobone, say) for this entity, nor can we easily track it over space and time. Why is it that Fido is a psychologically possible individual, but Fidobone is not? One answer is that Fido is a discrete physical object—and discrete physical objects are natural individuals. People count objects, track them, categorize them as belonging to different kinds, and learn names for these kinds. Psychologists typically concern themselves with objects when constructing theories of linguistic and noniinguistic capacities, and many theories of how we learn and understand words are restricted to the learning and understanding of object names, implicitly adopting the view that, for humans, individuals just are discrete whole objects. This view cannot be right, however. Children and adults do learn words such as chapter, party, and joke; we can count chapters, par-

Published hy Cambridge University i'ress

tory immune response Eo an oral antigen in men. Health Psychology, 13. 440-446.

Recommended Reading Cohen, S., & Herbert, T.B. (1996). Psychological factors and physical disease from the perspective of human psychoneuroimmunology. Annual Rn'iavof P., & Kelemen, D. (1995], Syntactic cues in the acquisition of collective nouns. Cognition, 56, 1-30, Bloom, P., Kelemen, 13,, Fountain, A., & Courtney, t,. (1995). The acquisition of colleclive nouns. In D. MacLaughlin & S. McEwen (Hds,), Proceedings of the 19th Boston lluivcrsity Conference oil Language Development. Boston; Cascadilla Press Bloom, P,, & Veres, C (1996), The perceived mtentionaUty of groups Manuscript submitted lor publication, Braddick, O.j, (1980) Low-level and highlevel processes in apparent motion. Philosophical Transactions of the Royal Society of London B, 290, 137-151, Carey, S. (1988), Conceptual differences between children and adults, .\4iiul aud Language, ^, 167-181. Heider, F,, & Simmel, M, (1944), An experimental study of apparent behavior, American journal of Psychology, 57, 243-239 Hoffman, ' D , D , , & Richards, W.A, (1984). Parts of recognition. Cognition, IS, 63-96. Leyton, M, (1992), Symmetry, causality, mind. Cambridge, MA; MIT Press, Markman, E.M. (1990) Constraints children

Integrating Information Across Saccadic Eye Movements David E. Irwin^ Department of Psychology, University of Illinois, Urbana-Champaign, Champaign, Illinois

We make rapid eye movements called saccades about three times each second in order to examine the world around us. The still periods between saccades are called fixations. The average fixation is approximately 300 ms in duration, whereas the average saccade is only 30 ms in duration. We make saccades in order to direct the fovea of the eye, which provides our clearest vision, at objects of interest in the environment. Sac-

cadic eye movements create problems for perception because visual information sweeps across the back of the eyes during each saccade; as a consequence, objects in the world have different positions on the retina from one fixation to the next. Even though the visual input is continually changing in this way, we ordinarily perceive the world as a coherent whole, with objects maintaining their positions in space. There is no feeling

Published by Cambridge University Press

place on word meanings. Cognitive Science, 14, 5777. Nelson, K., Hampson, ], , & Shaw, L,K, (1993). Nouns in early lexicons; Evidence, explanations, and extensions, journal of Child langiia^f, 20, 61-84. Shipley, E.E,, & S h e p p e r s o n , B, (1990), Countable entities; Developmental changes, Qi^'nition, 34, 11)9-136. Soja, N.N (1994), Evidence for a distinct type of noun Cognition, 51, 2h7~-2SA Spelke, E.S. (1994). Initial knowledge; Six suggestions, Cogiitlion, 50, 431^45, Spelke, E,S , Bieinlinger, K,, Jacobsoii, K,, & Phillips, A (1993). Geslalt relations and object perception: A developmental study Perception, :2, 1483-1501, Slarkey, i'., Spelke, E.S., & Celman, K. (199(3), Numerical abstracHon by human infants. CAigndion, 36, 97-127 Wynn, K. (1992). Evidence against empiricist accounts of the origin of numerical knowledge. Mind and Ltinguagc, 7, 313-332. Wynn, K, (1996). Infants' mdividuation and enumeration ot actions, Psycholoiiical Science, 7,

16^169,

Recommended Reading Bloom, P. (in press). Inlenlion, histor\, and arlifart concepts Cognition. Dennett, D 1199!). Real patterns, journal of Philosophy, S8, 27-r-l. Macnamara, |. (1994). Logic and cognition. In ), Macnamara & G E, Reyes (Eds.), The logical loiiudiittons of cognition (pp. 11- 34). Mew York: Oxford University Press, Spelke, E.S., Breinlinger, K., Macomber, j . , & lacobson, K. (1992). Origins ol knowledge Psychological Rerwu\ 99, 605-632,

of "starting anew" with each fixation; rather, we remember the positions and the identities of at least some of the objects in a scene, even if we close our eyes. Psychologists and vision researchers have wondered for more than a century how this quality of perception is achieved. One frequently proposed hypothesis is that visual information acquired during individual eye fixations is accumulated across saccades. This view assumes the existence of a transsaccadic memory that combines the information from successive eye fixations in such a way that a percept of a stable and continuous visual world is produced. In this article, I summarize research that my colleagues and 1 have conducted during the past 15 years to