Biomedical subjects

Sasan Mahmoodi

Publications and source records attributed to Sasan Mahmoodi.

4 recordsLinked to original sources

PubMed2005

Longer fixation duration while viewing face images.

The spatio-temporal properties of saccadic eye movements can be influenced by the cognitive demand and the characteristics of the observed scene. Probably due to its crucial role in social communication, it is argued that face perception may involve different cognitive processes compared with non-face object or scene perception. In this study, we investigated whether and how face and natural scene images can influence the patterns of visuomotor activity. We recorded monkeys' saccadic eye movements as they freely viewed monkey face and natural scene images. The face and natural scene images attracted similar number of fixations, but viewing of faces was accompanied by longer fixations compared with natural scenes. These longer fixations were dependent on the context of facial features. The duration of fixations directed at facial contours decreased when the face images were scrambled, and increased at the later stage of normal face viewing. The results suggest that face and natural scene images can generate different patterns of visuomotor activity. The extra fixation duration on faces may be correlated with the detailed analysis of facial features.

Analysis of Variance↗

PubMed2005

Centre-surround interactions in response to natural scene stimulation in the primary visual cortex.

Centre-surround interaction in the primary visual cortex (area V1) has been studied extensively using artificial, abstract stimulus patterns, such as bars, gratings and simple texture patterns. In this experiment, we extend the study of centre-surround interaction by using natural scene images. We systematically varied the contrast of natural image surrounds presented outside the classical receptive field (CRF), and recorded neuronal response to a natural image patch presented within the CRF in area V1 of awake, fixating macaques. For the majority of neurons (67 out of 111), the natural image surrounds profoundly modulated, mainly by suppressing, neuronal responses to CRF images. These modulatory effects started at the earliest stage of neuronal responses, and often depended on the contrast and higher-order structures of the surrounds. For 47 out of 67 neurons, randomising the phases of the Fourier spectrum of the natural image surround diminished the centre-surround interaction. Our results suggest that the centre-surround interaction in area V1 can be extended to natural vision, and is sensitive to the higher-order structures of natural scene images, such as image contours.

Action Potentials↗

PubMed2003

How do monkeys view faces?--A study of eye movements.

Face perception plays a crucial role in primate social communication. We have investigated the pattern of eye movements produced by rhesus monkeys (Macaca mulatta) as they viewed images of faces. Eye positions were recorded accurately using implanted eye coils, while neutral upright, inverted and scrambled images of monkey and human faces were presented on a computer screen. The monkeys exhibited a similar eye scan pattern while viewing familiar and unfamiliar monkey face images, or while viewing monkey and human face images. No differences were observed in the distribution of viewing times, number of fixations, time into the trial of first saccade to local facial features, and the temporal and spatial characteristics of viewing patterns across the facial images. However, there was a greater probability of re-fixation of the eye region of unfamiliar faces during the first few seconds of the trial suggesting that the eyes are important for the initial encoding of identity. Indeed, the highest fixation density was found in the eye region of all the face images. The viewing duration and the number of fixations per image decreased when inverted or scrambled faces were presented. The eye region in these modified images remained the primary area of fixation. However, the number of fixations directed to the eyes decreased monotonically from the upright images through the inverted versions to the scrambled face images. Nonetheless, the eyes remain the most salient facial substructure regardless of the arrangement of other features, although the extent of salience which they attain may depend both on the low level properties of the eyes and on the global arrangement of facial features.

Animals↗

PubMed2002

Human female attractiveness: waveform analysis of body shape.

Two putative cues to female physical attractiveness are body mass index (BMI) and shape (particularly the waist-hip ratio or WHR). To determine the relative importance of these cues we asked 23 male and 23 female undergraduates to rate a set of 60 pictures of real women's bodies in front-view for attractiveness. In our set of images, the relative ranges of BMI and WHR favoured WHR. We based these ranges on a sample of 457 women. We did not limit the WHR range, although we kept the BMI range to 0.5 s.d. either side of the sample means. As a result, WHR averaged 1.65 s.d. either side of its sample mean. However, even with these advantages, WHR was less important than BMI as a predictor of attractiveness ratings for bodies. BMI is far more strongly correlated with ratings of attractiveness than WHR (BMI approximately 0.5, WHR approximately 0.2). To further explore the relative importance of BMI and WHR, we deliberately chose a subset of these images that demonstrated an inverse correlation of BMI and WHR (i.e. a group in which as images get heavier they also become more curvaceous). If WHR is the most important determinant of attractiveness, then the more curvaceous (but higher BMI) images should be judged most attractive. However, if BMI is a better predictor, then the opposite should be true. We found that the more curvaceous (but higher BMI) images were judged least attractive, thereby inverting the expected rating pattern. This strongly suggests that viewers' judgements were influenced more by BMI than WHR. Finally, it is possible that body shape is an important cue to attractiveness, but that simple ratios (such as WHR) are not adequately capturing it. Therefore, we treated the outline of the torso as a waveform and carried out a set of waveform analyses on it to allow us to quantify body shape and correlate it with attractiveness. The waveform analyses address the complexity of the whole torso shape, and reveal innate properties of the torso shape and not shape elements based on prior decisions about arbitrary physical features. Our analyses decompose the waveform into objective quantified elements whose importance in predicting attractiveness can then be tested. All of the components that were good descriptors of body shape were weakly correlated with attractiveness. Our results suggest that BMI is a stronger predictor of attractiveness than WHR.

Adult↗