The mental representation of ordinal sequences is spatially organized

In the domain of numbers the existence of spatial components in the representation of numerical magnitude has been convincingly demonstrated by an association between number magnitude and response preference with faster left- than right-hand responses for small numbers and faster right- than left-hand responses for large numbers (Dehaene, S., Bossini, S., & Giraux, P. (1993) The mental representation of parity and number magnitude. Journal of Experimental Psychology: General, 122, 371-396). Because numbers convey not only real or integer meaning but also ordinal meaning, the question of whether non-numerical ordinal information is spatially coded naturally follows. While previous research failed to show an association between ordinal position and spatial response preference, we present two experiments involving months (Experiment 1) and letters (Experiment 2) in which spatial coding is demonstrated. Furthermore, the response-side effect was obtained with two different stimulus-response mappings. The association occurred both when ordinal information was relevant and when it was irrelevant to the task, showing that the spatial component of the ordinal representation can be automatically activated.     

Evidence for the substantia nigra pars compacta as an essential component of a memory system independent of the hippocampal memory system

The aim of the present study was to test if the nigrostriatal pathway is an essential component for a water maze cued task learning and if it works independently of the hippocampal memory system. This hypothesis was tested using an animal model of Parkinson's disease in which male Wistar rats were lesioned in the substantia nigra pars compacta (SNc) by the intranigral infusion of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), thus causing a partial depletion of striatal dopamine. SNc-lesioned and sham-operated animals were implanted bilaterally with guide cannulae above the dorsal hippocampus in order to be tested after the administration of 0.4 microl 2% lidocaine or saline into this structure. The animals were tested in a spatial or in a cued version of the water maze, memory tasks previously reported to model hippocampal-dependent spatial/relational and striatal-dependent S-R learning, respectively. Hippocampal inactivation, but not SNc lesion, impaired learning and memory in the spatial version of the water maze. An opposite situation was observed with the cued version. No significant interaction was observed between the SNc lesion and hippocampal inactivation conditions affecting scores in the spatial or in the cued version of the water maze. These results suggest that the nigrostriatal pathway is an essential part of the memory system that processes S-R learning and that it works independently of the hippocampal memory system that processes spatial/relational memories.     

Short-term estrogen treatment in ovariectomized rats augments hippocampal acetylcholine release during place learning

Estrogen modulates learning and memory in ovariectomized and naturally cycling female rats, especially in tasks using spatial learning and navigation. Estrogen also modulates cholinergic function in various forebrain structures. Past studies have shown positive correlations between hippocampal ACh output and performance on hippocampus-dependent tasks. The present study examined whether estradiol replacement would potentiate hippocampal ACh release during place learning. In vivo microdialysis and HPLC were used to measure extracellular ACh levels in the hippocampus of ovariectomized female rats that had received s.c. injections of 17beta-estradiol (10 microg) or sesame oil (vehicle treatment) 48 and 24h prior to training on a place task. Estrogen did not alter baseline levels of extracellular ACh in the hippocampus. During training, hippocampal ACh increased in ovariectomized rats regardless of estrogen status. However, while estradiol did not enhance learning in this experiment, estradiol significantly potentiated the increase in hippocampal ACh release seen during place training. This represents the first demonstration of on-line assessment of ACh output in hippocampus during learning in female rats and suggests that estrogen-dependent modulation of ACh release during training might control activation of different neural systems used during learning.     

Strategic navigation of two-dimensional alley mazes: comparing capuchin monkeys and chimpanzees

Planning is an important component of cognition that contributes, for example, to efficient movement through space. In the current study we presented novel two-dimensional alley mazes to four chimpanzees and three capuchin monkeys to identify the nature and efficiency of planning in relation to varying task parameters. All the subjects solved more mazes without error than expected by chance, providing compelling evidence that both species planned their choices in some manner. The probability of making a correct choice on mazes designed to be more demanding and presented later in the testing series was higher than on earlier, simpler mazes (chimpanzees), or unchanged (capuchin monkeys), suggesting microdevelopment of strategic choice. Structural properties of the mazes affected both species' choices. Capuchin monkeys were less likely than chimpanzees to take a correct path that initially led away from the goal but that eventually led to the goal. Chimpanzees were more likely to make an error by passing a correct path than by turning onto a wrong path. Chimpanzees and one capuchin made more errors on choices farther in sequence from the goal. Each species corrected errors before running into the end of an alley in approximately 40% of cases. Together, these findings suggest nascent planning abilities in each species, and the prospect for significant development of strategic planning capabilities on tasks presenting multiple simultaneous or sequential spatial relations. The computerized maze paradigm appears well suited to investigate movement planning and spatial perception in human and nonhuman primates alike.     

Object-goal positioning influences spatial representation in rats

Three tests investigated how the geometric relation between object/landmarks and goals influenced spatial choice behavior in rats. Two groups searched for hidden food in an object-filled circular arena containing 24 small poles. For the “Proximal” group, four distinct objects in a square configuration were placed close to four baited poles. For the “Distal” group, the identical configuration of objects was rotated 45° relative to the poles containing the hidden food. The Proximal group learned to locate the baited poles more quickly than the Distal group. Tests with removed and rearranged landmarks indicated that the two groups learned to use the objects differently. The results suggested that close proximity of objects to goals encouraged their use as beacons, while greater distance of objects from goals resulted in the global encoding of the geometric properties of the arena and the use of the objects as landmarks. Received: 22 June 1998 / Accepted after revision: 23 January 1999     

Sun compass orientation in seed-caching corvids: its role in spatial memory

The role of sun compass orientation in spatial memory of Clark’s nutcrackers, Nucifraga columbiana, and pinyon jays, Gymnorhinus cyanocephalus, was studied in a series of cache recovery experiments. Birds were tested in an octagonal outdoor aviary with sand-filled cups inserted in the floor. For caching, only 12 such cups in a 90° sector were available, while for recovery 4–7 days later all 48 cups in the entire aviary were open. In control tests, the birds concentrated their search activity in the sector where they had cached. When their internal clock was shifted 6 h between caching and recovery, pinyon jays shifted their search activity to the 90° adjacent sector, as predicted if the sun compass was used. Clark’s nutcrackers did not respond to the first clock-shift; however, they, too, shifted their search activity after a second clock-shift back to normal. This suggests that the sun compass is a component of spatial memory in both species. Clark’s nutcrackers, however, seem to rely on their sun compass to a lesser degree than pinyon jays or the previously studied scrub jays. A comparison of the findings indicates that the role of the sun in spatial memory might reflect differences in habitat and ecology of the three corvid species. Received: 18 February 1999 / Accepted after revision: 17 September 1999     

Spatial representation of pitch height: the SMARC effect

Through the preferential pairing of response positions to pitch, here we show that the internal representation of pitch height is spatial in nature and affects performance, especially in musically trained participants, when response alternatives are either vertically or horizontally aligned. The finding that our cognitive system maps pitch height onto an internal representation of space, which in turn affects motor performance even when this perceptual attribute is irrelevant to the task, extends previous studies on auditory perception and suggests an interesting analogy between music perception and mathematical cognition. Both the basic elements of mathematical cognition (i.e. numbers) and the basic elements of musical cognition (i.e. pitches), appear to be mapped onto a mental spatial representation in a way that affects motor performance.     

Returning the tables: language affects spatial reasoning

Li and Gleitman (Turning the tables: language and spatial reasoning. Cognition, in press) seek to undermine a large-scale cross-cultural comparison of spatial language and cognition which claims to have demonstrated that language and conceptual coding in the spatial domain covary (see, for example, Space in language and cognition: explorations in linguistic diversity. Cambridge: Cambridge University Press, in press; Language 74 (1998) 557): the most plausible interpretation is that different languages induce distinct conceptual codings. Arguing against this, Li and Gleitman attempt to show that in an American student population they can obtain any of the relevant conceptual codings just by varying spatial cues, holding language constant. They then argue that our findings are better interpreted in terms of ecologically-induced distinct cognitive styles reflected in language. Linguistic coding, they argue, has no causal effects on non-linguistic thinking--it simply reflects antecedently existing conceptual distinctions. We here show that Li and Gleitman did not make a crucial distinction between frames of spatial reference relevant to our line of research. We report a series of experiments designed to show that they have, as a consequence, misinterpreted the results of their own experiments, which are in fact in line with our hypothesis. Their attempts to reinterpret the large cross-cultural study, and to enlist support from animal and infant studies, fail for the same reasons. We further try to discern exactly what theory drives their presumption that language can have no cognitive efficacy, and conclude that their position is undermined by a wide range of considerations.