Synaesthesia: the prevalence of atypical cross-modal experiences

Sensory and cognitive mechanisms allow stimuli to be perceived with properties relating to sight, sound, touch, etc, and ensure, for example, that visual properties are perceived as visual experiences, rather than sounds, tastes, smells, etc. Theories of normal development can be informed by cases where this modularity breaks down, in a condition known as synaesthesia. Conventional wisdom has held that this occurs extremely rarely (0.05% of births) and affects women more than men. Here we present the first test of synaesthesia prevalence with sampling that does not rely on self-referral, and which uses objective tests to establish genuineness. We show that (a) the prevalence of synaesthesia is 88 times higher than previously assumed, (b) the most common variant is coloured days, (c) the most studied variant (grapheme-colour synaesthesia)--previously believed most common--is prevalent at 1%, and (d) there is no strong asymmetry in the distribution of synaesthesia across the sexes. Hence, we suggest that female biases reported earlier likely arose from (or were exaggerated by) sex differences in self-disclosure.     

Reversing how to think about ambiguous figure reversals: spontaneous alternating by uninformed observers

Ambiguous figures are a special class of images that can give rise to multiple interpretations. Traditionally, switching between the possible interpretations of an ambiguous figure, or reversing one's interpretation, has been attributed either to top-down or to bottom-up processes (e.g. attributed to having knowledge of the nature of the ambiguity, or to a form of neuronal fatigue). Here we present evidence that is incompatible with both forms of explanations. Observers aged 5-9 years can reverse ambiguous figures when uninformed about the ambiguity, negating purely top-down explanations. Further, those children who make these 'spontaneous' reversals are more likely to succeed on a high-order theory-of-mind task, negating purely bottom-up explanations.     

A theory of causal learning in children: causal maps and Bayes nets

The authors outline a cognitive and computational account of causal learning in children. They propose that children use specialized cognitive systems that allow them to recover an accurate "causal map" of the world: an abstract, coherent, learned representation of the causal relations among events. This kind of knowledge can be perspicuously understood in terms of the formalism of directed graphical causal models, or Bayes nets. Children's causal learning and inference may involve computations similar to those for learning causal Bayes nets and for predicting with them. Experimental results suggest that 2- to 4-year-old children construct new causal maps and that their learning is consistent with the Bayes net formalism.     

Lion Kings or puppies: the influence of fantasy on children’s understanding of pretense

Many have thought that children have an early appreciation of the mind in the case of pretend play. Results from several experiments are against this. However, an experiment by Lillard (Body or mind: children’s categorizing of pretense, Child Development, 67 (1996), 1717-1734, Experiment 4) suggested that when a pretense is about a fantasy character, instead of a real entity, children might have a better understanding of the mind’s involvement. The present experiment tested this, and found that indeed, when pretending to be a fantasy character is at issue, 4-year-olds are significantly more apt to indicate the mind’s involvement. Several possible reasons for this result are discussed.     

What-where-when memory in pigeons

The authors report a novel approach to testing episodic-like memory for single events. Pigeons were trained in separate sessions to match the identity of a sample on a touch screen, to match its location, and to report on the length of the retention interval. When these 3 tasks were mixed randomly within sessions, birds were more than 80% correct on each task. However, performance on 2 different tests in succession after each sample was not consistent with an integrated memory for sample location, time, and identity. Experiment 2 tested binding of location and identity memories in 2 different ways. The results were again consistent with independent feature memories. Implications for tests of episodic-like memory are discussed.     

How context influences predominance during binocular rivalry

Variations in the predominance of an object engaged in binocular rivalry may arise from variations in the durations of dominance phases, suppression phases, or both. Earlier work has shown that the predominance of a binocular rival target is enhanced if that target fits well-via common color, orientation, or motion-with its surrounding objects. In the present experiments, the global context outside of the region of rivalry was changed during rivalry, to learn whether contextual information alters the ability to detect changes in a suppressed target itself. Results indicate that context will maintain the dominance of a rival target, but will not encourage a suppressed target to escape from suppression. Evidently, the fate of the suppressed stimulus is determined by neural events distinct from those responsible for global organization during dominance. To reconcile diverse findings concerning rivalry, it may be important to distinguish between processes responsible for selection of one eye's input for dominance from processes responsible for the implementation and maintenance of suppression.     

Causal learning mechanisms in very young children: two-, three-, and four-year-olds infer causal relations from patterns of variation and covariation

Three studies investigated whether young children make accurate causal inferences on the basis of patterns of variation and covariation. Children were presented with a new causal relation by means of a machine called the "blicket detector." Some objects, but not others, made the machine light up and play music. In the first 2 experiments, children were told that "blickets make the machine go" and were then asked to identify which objects were "blickets." Two-, 3-, and 4-year-old children were shown various patterns of variation and covariation between two different objects and the activation of the machine. All 3 age groups took this information into account in their causal judgments about which objects were blickets. In a 3rd experiment, 3- and 4-year-old children used the information when they were asked to make the machine stop. These results are related to Bayes-net causal graphical models of causal learning.     

Learning about environmental geometry: an associative model

K. Cheng (1986) suggested that learning the geometry of enclosing surfaces takes place in a geometric module blind to other spatial information. Failures to find blocking or overshadowing of geometry learning by features near a goal seem consistent with this view. The authors present an operant model in which learning spatial features competes with geometry learning, as in the Rescorla-Wagner model. Relative total associative strength of cues at a location determines choice of that location and thus the frequencies of reward paired with each cue. The model shows how competitive learning of local features and geometry can appear to result in potentiation, blocking, or independence, depending on enclosure shape and kind of features. The model reproduces numerous findings from dry arenas and water mazes.     

Individual differences in working memory capacity and visual search: The roles of top-down and bottom-up processing

Individual differences in working memory capacity (WMC) have been implicated in a variety of top-down, attention-control tasks: Higher WMC subjects better ignore irrelevant distractions and withhold habitual responses than do lower WMC subjects. Kane, Poole, Tuholski, and Engle (2006) recently attempted to extend these findings to visual search, but found no relation between WMC and search efficiency, even in difficult tasks yielding steep search slopes. Here we used a visual search task that isolated the contributions of top-down versus bottom-up mechanisms, and induced a habitual response via expectation. Searches that relied primarily on bottom-up mechanisms did not vary with WMC, but searches that relied primarily on top-down mechanisms showed an advantage for higher over lower WMC subjects.