Delayed recall of fear extinction in rats with lesions of ventral medial prefrontal cortex

Extinction of auditory fear conditioning is thought to form a new memory. We previously found that rats with vmPFC lesions could extinguish fear to the tone within a session, but showed no recall of extinction 24 h later. One interpretation is that the vmPFC is the sole storage site of extinction memory. However, it is also possible that lesioned rats were unable to retrieve extinction memory stored in other structures. To determine if a latent extinction memory could be retrieved with additional training, we repeated the experiment but added an additional 5 d of extinction reminder trials. Replicating our previous findings, vmPFC-lesioned rats extinguished normally on day 1, but showed no recall of extinction on day 2. Over the next 5 d, however, lesioned rats showed significant savings in their rate of re-extinction. Thus, the vmPFC is not the only site where extinction memory is stored. Nevertheless, lesioned rats receiving only two extinction trials per day required twice as many days to initiate extinction as controls. Although recall of extinction is possible without the vmPFC, it is significantly delayed. We suggest that the vmPFC accelerates extinction by permitting access to recently learned extinction trials, thereby maximizing behavioral flexibility.     

Are readers of our face readers of our minds? Dogs (<Emphasis Type="Italic">Canis familiaris</Emphasis>) show situation-dependent recognition of human’s attention

The ability of animals to use behavioral/facial cues in detection of human attention has been widely investigated. In this test series we studied the ability of dogs to recognize human attention in different experimental situations (ball-fetching game, fetching objects on command, begging from humans). The attentional state of the humans was varied along two variables: (1) facing versus not facing the dog; (2) visible versus non-visible eyes. In the first set of experiments (fetching) the owners were told to take up different body positions (facing or not facing the dog) and to either cover or not cover their eyes with a blindfold. In the second set of experiments (begging) dogs had to choose between two eating humans based on either the visibility of the eyes or direction of the face. Our results show that the efficiency of dogs to discriminate between attentive and inattentive humans depended on the context of the test, but they could rely on the orientation of the body, the orientation of the head and the visibility of the eyes. With the exception of the fetching-game situation, they brought the object to the front of the human (even if he/she turned his/her back towards the dog), and preferentially begged from the facing (or seeing) human. There were also indications that dogs were sensitive to the visibility of the eyes because they showed increased hesitative behavior when approaching a blindfolded owner, and they also preferred to beg from the person with visible eyes. We conclude that dogs are able to rely on the same set of human facial cues for detection of attention, which form the behavioral basis of understanding attention in humans. Showing the ability of recognizing human attention across different situations dogs proved to be more flexible than chimpanzees investigated in similar circumstances.     

Determinants of picture naming times in Icelandic

Numerous studies have found that word frequency has a significant effect on the time it takes to name an object or read a word. Recently, claims have been made that this frequency effect is perhaps more correctly interpreted as an age of acquisition effect. This paper reports an experiment in which naming times in Icelandic for 175 stimuli from the Snodgrass and Vanderwart picture set were determined. A multiple regression analysis of naming times against a number of independent factors showed that objective age of acquisition was the strongest predictor of naming time, with familiarity and name agreement also showing a significant effect. The effect of word frequency was, however, not significant. Possible reasons for this are discussed.     

Effect of the similarity between target and global and local levels in hierarchical stimuli processing

The hypothesis of global precedence was investigated by manipulating the similarity between target and relevant level, and between target and global and local levels of hierarchical stimuli, both in divided and selective attention conditions. The similarity was measured on the basis of the amount of shared contour between two visual forms. The stimuli were circles, right-facing semicircles, i.e., 1/2 of the circumference missing, and right-facing partial circles with a 1/4 of the circumference missing. The circle was used as a target and, consequently, the similarity between target and semicircle and between it and the partial circle was 50% and 75%, respectively. In the divided attention condition, the results showed a local advantage in the two similarity conditions between target and distractor level (50% and 75%) and a bidirectional and symmetrical interference at both levels of similarity. However, in the 'selective attention condition', a local reaction time advantage was only found when the similarity between target and irrelevant level was of 50%. When attention was directed towards the global level, local interference increased depending on the decrease in the degree of the local level similarity. When the attention was directed towards the local level, there was global interference but it was independent of the degree of the global level similarity. These results show the importance of the physical shape of the local elements used in experiments with hierarchical stimuli, since they may determine the relative speed of global processing, facilitating or impairing it.     

Preference for copying unambiguous demonstrations in dogs (Canis familiaris)

In an earlier study (P. Pongracz et al., 2001), it was shown that human demonstration significantly enhances the detouring ability of dogs (Canis familiaris) around a V-shaped fence. The authors investigated the effect of the direction of the demonstrated detour and the dogs' detouring experience. They found that dogs' trial-and-error experience influences strongly the direction of the dogs' detours later, even if the demonstrator showed detours along the opposite side of the fence. However, dogs' preferences based on their own experiences were changed when the dogs observed demonstrations only on 1 side of the fence. Dogs with no trial-and-error experience followed the direction of 1-sided demonstrations. The change from dogs' own directions to the demonstrated directions seems not to be due to simple facilitative effects of social experience; the similarity with the demonstrated action depends on complex interactions between individual experience and socially provided information.     

The PIG in sPrInG: Evidence on letter grouping from the reading of buried words

We introduce a novel procedure for investigating factors that determine selective attention to letters in words. Participants were presented with words (in Experiments 1 and 3) and nonwords (in Experiment 2) that contained a buried word whose letters differed in color relative to the other letters present (e.g.,pig, in spring). The strings were presented in single case or mixed case, keeping the letters of the buried words in one case (SpRiNg). The time in which the whole stimulus was named was shorter for same-case than for mixed-case strings (forspring: spring < SpRiNg). In contrast, the time in which buried words were named was shorter in mixed- than in same-case strings (forpig: spring > SpRiNg). Across items, the effects of case mixing were negatively correlated across the two tasks. The positive effect of case mixing for buried words also occurred irrespective of whether the whole string was a word or a nonword, and there were contributions from similarity of both letter size and case. The results suggest that case mixing can facilitate selective attention to letters, which is otherwise disrupted by size- and case-based grouping across letter strings. The study provides evidence for letter grouping using size and case information.     

Age-related changes and gender differences in time estimation

A study was carried out in which age and gender differences were studied in the performance of an empty interval production task. The duration of these intervals was 10 s, 1 and 5 min. The sample was made up of 140 subjects, half male and half female, in seven different age groups from 8 to 70 years old. The age range permitted us to identify when differences begin to be significant. The results show an age-related increase in the underproduction of the intervals. The differences between age groups attained significance from 51 to 60 years onward. With regard to gender, the main result was a greater underproduction of longer intervals (1 and 5 min) for women. These findings were interpreted in terms of different models of time estimation.