Comparative and categorical spatial judgments in the monkey: “high” and “low”

Adult human subjects can classify the height of an object as belonging to either of the high or low categories by utilizing an abstract concept of midline that divides the vertical dimension into two halves. Children lack this abstract concept of midline, do not have a sense that these categories are directional opposites, and their categorical and comparative usages of high(er) or low(er) are restricted to the corresponding poles. We investigated the abilities of a rhesus monkey to perform categorical judgments in space. We were also interested in the presence of the congruity effect (a decrease in response time when the objects compared are closer to the category pole) in the monkey. The presence of this phenomenon in the monkey would allow us to relate the behavior of the animal to the two major competing hypotheses that have been suggested to explain the congruity effect in humans: the analog and semantic models. The monkey was trained in delayed match-to-sample tasks in which it had to categorize objects as belonging to either a high or low category. The monkey was able to generate an abstract notion of midline in a fashion similar to that of adult human subjects. The congruity effect was also present in the monkey. These findings, taken together with the notion that monkeys are not considered to think in propositional terms, may favor an analog comparison model in the monkey.     

Object localisation and frames of reference

In this paper, we explore which spatial frames of reference, egocentric or allocentric, are used to locate objects either in relation to ourselves (i.e. subject-to-object localisation) or to other objects (i.e. object-to-object localisation). In particular, we wanted to know whether the same or different frames of reference are used in these two different kinds of localisation after learning the environment in an egocentric way. Egocentric frames of reference are determined by the position of the person in relation to the spatial layout, whereas allocentric frames of reference are centred on the environment or on objects, independent of a persons position. We hypothesised that subject-to-object localisation is based on egocentric spatial representations, whereas object-to-object localisation is based on allocentric spatial representations. Participants were asked to study eight common objects, placed in a circle. Next, half of the participants had to point to an object in relation to their imagined position (egocentric condition) and the other half to an object in relation to another object (allocentric condition). The overall results show no difference between subject-to-object and object-to-object localisation. In both cases, access to positions corresponding to the front/back body axis was facilitated, in terms of both latency and error. Moreover, participants were able to retrieve objects positions better from the perspective from which they had learned the spatial array than from new perspectives. These results support the conclusion that egocentric coordinates, which are selected on the basis of our body-centred experience of the environment, define spatial representations underlying both subject-to-object and object-to-object localisation.     

Changing perspective within and across environments

Perspective change within a single environment is a slow and effortful process. However, little research has addressed perspective change across multiple environments. Using a task-set switching paradigm, subjects judged spatial relationships between target locations from differing perspectives. Response times were longer when successive trials probed different perspectives. However, this cost was greater when perspective was changed within a single environment compared to when it was changed across two environments. This result indicates that the processing of perspective change, and perhaps general spatial reasoning, differs in these two cases. Implications for theories of perspective change and environmental knowledge are discussed.     

Estrogen modulates place learning through estrogen receptors in the hippocampus

Moderate elevations in circulating estradiol enhance learning in tasks that tap place learning strategies such as those requiring the use of extramaze cues. Use of place learning strategies is particularly impaired by damage to the hippocampus, a structure shown to be sensitive to estrogen treatments. We have shown that direct estrogen infusions into the dorsal hippocampus, and not the dorsolateral striatum, enhance place learning, suggesting that the hippocampus may be an important modulatory site for the effects of estrogen on place learning. The current experiment tested whether the hippocampus is indeed a critical site of estrogen modulation through classical estrogen receptors. Young adult female Sprague-Dawley rats were ovariectomized for 21 days and given systemic injections (0.1 ml) of sesame oil (OIL) or 10 microg of 17beta-estradiol-benzoate (E2), 48 and 24 h before being trained on a place task. Twenty-four hours prior to the first systemic injection, separate groups of rats received bilateral hippocampal implants of either the antiestrogen ICI 182,780 (ICI) or cholesterol vehicle. Implants were maintained until and throughout training. Intrahippocampal ICI reversed the enhancement in place learning seen with systemic E2 treatment. Unexpectedly, intrahippocampal ICI in OIL-treated rats also enhanced place learning. These data suggest that ICI may have some mixed agonist and antagonist effects in the hippocampus and that estrogen enhances place learning through activation of estrogen receptors located in the hippocampus.     

Multiple landmarks, the encoding of environmental geometry and the spatial logics of a dual brain

A series of place learning experiments was carried out in young chicks (Gallus gallus) in order to investigate how the geometry of a landmark array and that of a walled enclosure compete when disoriented animals could rely on both of them to re-orient towards the centre of the enclosure. A square-shaped array (four wooden sticks) was placed in the middle of a square-shaped enclosure, the two structures being concentric. Chicks were trained to ground-scratch to search for food hidden in the centre of the enclosure (and the array). To check for effects of array degradation, one, two, three or all landmarks were removed during test trials. Chicks concentrated their searching activity in the central area of the enclosure, but their accuracy was inversely contingent on the number of landmarks removed; moreover, the landmarks still present within the enclosure appeared to influence the shape of the searching patterns. The reduction in the number of landmarks affected the searching strategy of chicks, suggesting that they had focussed mainly on local cues when landmarks were present within the enclosure. When all the landmarks were removed, chicks searched over a larger area, suggesting an absolute encoding of distances from the local cues and less reliance on the relationships provided by the geometry of the enclosure. Under conditions of monocular vision, chicks tended to rely on different strategies to localize the centre on the basis of the eye (and thus the hemisphere) in use, the left hemisphere attending to details of the environment and the right hemisphere attending to the global shape.This contribution is part of the special issue “Animal Logics” (Watanabe and Huber 2006).     

Top-down contingent capture by color: evidence from RT distribution analyses in a manual choice reaction task

According to the contingent capture hypothesis, observers can specify their control settings in advance of the target’s presentation to quickly attend to relevant target colors. Two predictions were derived from this hypothesis and tested in a manual choice response task. First, contingent capture by color was expected: capture of spatial attention by a better-matching color stimulus should be stronger than capture by a less-matching color stimulus. Second, with the control settings specified in advance, the contingent capture by color should commence early after the stimulus onset and should be evident among fast correct responses in an RT distribution. Both predictions are shown to hold true in two experiments. Results are discussed in light of contrasting evidence for saccadic instead of manual responses.     

Differentiation of classical music requires little learning but rhythm

Detecting distinctions between the styles of classical music (e.g. Baroque and Romantic) is often viewed as the privilege of musicians. However, this elite perspective underestimates the abilities of non-musicians. We report that Western musicians and non-musicians, and non-Westerners (i.e. Chinese participants) rated pairs of excerpts presented auditorily as more similar as their compositional styles were closer in history. Moreover, the styles were considered by all participants as more different when presented in historical order, the older style preceding the more recent style (e.g. Baroque followed by Romantic), than the reverse (e.g. Romantic followed by Baroque). This historical distance effect appears related to rhythm (or temporal variability).     

Canceling out both the real and the spectral lines

Neglect patients typically show motor perseveration while canceling targets on the ipsilesional side. This behavior can be influenced by the presence vs. absence of targets on the (neglected) contralesional side (). As alternative explanations, the authors proposed (i) directional hypokinesia--the patient cannot perform reaching movements towards detected left-sided targets, and thus carries on canceling on the right side, and (ii) allochiria--the patient misperceives left-sided targets as located on the right side, and cancels them there. We report here data from a patient (EZ) that might confirm the second hypothesis. EZ was presented with 19 displays in which the number and position of cancellation targets on both sides were varied systematically. EZ showed motor perseveration while canceling, but this tendency did not vary across conditions. Interestingly though, EZ also drew cancellation marks in the empty space between the ipsilesional targets, and this phenomenon was significantly more intense when there were more targets on the neglected side. As EZ's comments suggested, such a behavior might reflect the attempt to cancel out delusional targets. Our speculation is that those objects were generated by allochiria.