Local contrast in natural images: normalisation and coding efficiency

The visual system employs a gain control mechanism in the cortical coding of contrast whereby the response of each cell is normalised by the integrated activity of neighbouring cells. While restricted in space, the normalisation pool is broadly tuned for spatial frequency and orientation, so that a cell's response is adapted by stimuli which fall outside its 'classical' receptive field. Various functions have been attributed to divisive gain control: in this paper we consider whether this output nonlinearity serves to increase the information carrying capacity of the neural code. 46 natural scenes were analysed with the use of oriented, frequency-tuned filters whose bandwidths were chosen to match those of mammalian striate cortical cells. The images were logarithmically transformed so that the filters responded to a luminance ratio or contrast. In the first study, the response of each filter was calibrated relative to its response to a grating stimulus, and local image contrast was expressed in terms of the familiar Michelson metric. We found that the distribution of contrasts in natural images is highly kurtotic, peaking at low values and having a long exponential tail. There is considerable variability in local contrast, both within and between images. In the second study we compared the distribution of response activity before and after implementing contrast normalisation, and noted two major changes. Response variability, both within and between scenes, is reduced by normalisation, and the entropy of the response distribution is increased after normalisation, indicating a more efficient transfer of information.     

Mothers' depressed mood and anxiety levels are reduced after massaging their preterm infants

Forty mothers whose preterm infants were about to be discharged from the Neonatal Intermediate Care Nursery (NICU) were randomly assigned to two groups: the first group of mothers conducted preterm infant massage and the second group only observed their preterm infants receiving massage. Both groups of mothers had lower depressed mood scores following the session. However, only the group who massaged their infants had lower anxiety scores after the session.     

Prenatal depression effects on the fetus and newborn: a review

A review of research on prenatal depression effects on the fetus and newborn suggests that they experience prenatal, perinatal and postnatal complications. Fetal activity is elevated, prenatal growth is delayed, and prematurity and low birthweight occur more often. Newborns of depressed mothers then show a biochemical/physiological profile that mimics their mothers' prenatal biochemical/physiological profile including elevated cortisol, lower levels of dopamine and serotonin, greater relative right frontal EEG activation and lower vagal tone. Elevated prenatal maternal cortisol is the strongest predictor of these neonatal outcomes. Moderate pressure massage can alleviate these effects including reducing prematurity.     

Dissociating the effects of attention and contingency awareness on evaluative conditioning effects in the visual paradigm

Two experiments are described that investigate the effects of attention in moderating evaluative conditioning (EC) effects in a picture-picture paradigm in which previously discovered experimental artifacts (e.g., Field & Davey, 1999 ) were overcome by counterbalancing conditioned stimuli (CSs) and unconditioned stimuli (USs) across participants. Conditioned responses for individuals who had attention enhanced were compared against a control group and groups for whom attention was impeded using a distracter task. In a second experiment the effects of attention were dissociated from those of contingency awareness by using backward-masked US presentations. The results of these experiments indicate that although associative EC effects may not be disrupted by a lack of contingency awareness, attention is an important factor in establishing conditioning. These results shed some light onto the possible boundary conditions that could explain past inconsistencies in obtaining EC effects in the visual paradigm.     

The perception of emotion from body movement in point-light displays of interpersonal dialogue

We examined whether it is possible to identify the emotional content of behaviour from point-light displays where pairs of actors are engaged in interpersonal communication. These actors displayed a series of emotions, which included sadness, anger, joy, disgust, fear, and romantic love. In experiment 1, subjects viewed brief clips of these point-light displays presented the right way up and upside down. In experiment 2, the importance of the interaction between the two figures in the recognition of emotion was examined. Subjects were shown upright versions of (i) the original pairs (dyads), (ii) a single actor (monad), and (iii) a dyad comprising a single actor and his/her mirror image (reflected dyad). In each experiment, the subjects rated the emotional content of the displays by moving a slider along a horizontal scale. All of the emotions received a rating for every clip. In experiment 1, when the displays were upright, the correct emotions were identified in each case except disgust; but, when the displays were inverted, performance was significantly diminished for some emotions. In experiment 2, the recognition of love and joy was impaired by the absence of the acting partner, and the recognition of sadness, joy, and fear was impaired in the non-veridical (mirror image) displays. These findings both support and extend previous research by showing that biological motion is sufficient for the perception of emotion, although inversion affects performance. Moreover, emotion perception from biological motion can be affected by the veridical or non-veridical social context within the displays.     

Fear information and social phobic beliefs in children: a prospective paradigm and preliminary results

This paper presents a first attempt to develop a prospective paradigm to test Rachman's (Behav. Res. Ther. 15 (1977) 375) theory of fear acquisition for social fears. Following the prospective paradigm for animal fears developed by Field et al. (Behav. Res. Ther. 39 (2001) 1259) an attempt is made to adapt this paradigm to look at the effect of fear information in the development of social fears. A large group of normal children (N=135) who were at an age (10-13 years) at which social concerns are most pertinent were tested using this paradigm. They were given positive, negative or neutral information about three social situations: public speaking, eating in public, and meeting a new group of children. Children's fear beliefs were measured before and after the information was given and the information was given by a teacher, a same age peer or no information was given (a control). The results indicate that although information can change social fear beliefs it is dependent upon the type of social activity and who provides the information. The implications of these initial results for our understanding of both the role of fear information in the development of social fear beliefs, and the limitations of this current paradigm are discussed.     

Prism adaptation to dynamic events

In the present study, we explored adaptation to prism-displaced dynamic and static events under conditions of minimal information. Many of our interactions with the world are dynamic and involve reaching for or intercepting moving objects. The consequences (or feedback) of those interactions entail the presence or absence of physical contact with the moving objects. In this study, humans learned, with only heptic feedback, to intercept optically displaced falling balls. To eliminate visual feedback, the falling balls disappeared behind an occluder (which systematically varied in size across groups) prior to either striking or missing a subject's hand. As occluder size decreased, adaptation increased. With minimum occluder sizes, the greatest adaptation occurred around the training position, and adaptation decreased as distance between training and testing positions increased. The results can best be described in terms of a generalization gradient centered around the training position. This generalization gradient was not present when subjects were trained with ecologically similar static arrays. Implications for models of adaptation are discussed.