Effects of Specular Highlights on Perceived Surface Convexity

Shading is known to produce vivid perceptions of depth. However, the influence of specular highlights on perceived shape is unclear: some studies have shown that highlights improve quantitative shape perception while others have shown no effect. Here we ask how specular highlights combine with Lambertian shading cues to determine perceived surface curvature, and to what degree this is based upon a coherent model of the scene geometry. Observers viewed ambiguous convex/concave shaded surfaces, with or without highlights. We show that the presence/absence of specular highlights has an effect on qualitative shape, their presence biasing perception toward convex interpretations of ambiguous shaded objects. We also find that the alignment of a highlight with the Lambertian shading modulates its effect on perceived shape; misaligned highlights are less likely to be perceived as specularities, and thus have less effect on shape perception. Increasing the depth of the surface or the slant of the illuminant also modulated the effect of the highlight, increasing the bias toward convexity. The effect of highlights on perceived shape can be understood probabilistically in terms of scene geometry: for deeper objects and/or highly slanted illuminants, highlights will occur on convex but not concave surfaces, due to occlusion of the illuminant. Given uncertainty about the exact object depth and illuminant direction, the presence of a highlight increases the probability that the surface is convex.     

Vocal-auditory functions of the chimpanzee: consonant perception

The perception of consonants which were followed by the vowel [a] was studied in chimpanzees and humans, using a reaction time task in which reaction times for discrimination of syllables were taken as an index of similarity between consonants. Consonants used were 20 natural French consonants and six natural and synthetic Japanese stop consonants. Cluster and MDSCAL analyses of reaction times for discrimination of the French consonants suggested that the manner of articulation is the major determinant of the structure of the perception of consonants by the chimpanzees. Discrimination of stop consonants suggested that the major grouping in the chimpanzees was by voicing. The place of articulation from the lips to the velum was reproduced only in the perception of the synthetic unvoiced stop consonants in the two dimensional MDSCAL space. The phoneme-boundary effect (categorical perception) for the voicing and place-of-articulation features was also examined by a chimpanzee using synthetic [ga]-[ka] and [ba]-[da] continua, respectively. The chimpanzee showed enhanced discriminability at or near the phonetic boundaries between the velar voiced and unvoiced and also between the voiced bilabial and alveolar stops. These results suggest that the basic mechanism for the identification of consonants in chimpanzees is similar to that in humans, although chimpanzees are less accurate than humans in discrimination of consonants.     

Vocal-auditory functions in the chimpanzee: Vowel perception

The perception of vowels was studied in chimpanzees and humans, using a reaction time task in which reaction times for discrimination of vowels were taken as an index of similarity between vowels. Vowels used were five synthetic and natural Japanese vowels and eight natural French vowels. The chimpanzees required long reaction times for discrimination of synthetic [i] from [u] and [e] from [o], that is, they need long latencies for discrimination between vowels based on differences in frequency of the second formant. A similar tendency was observed for discrimination of natural [i] from [u]. The human subject required long reaction times for discrimination between vowels along the first formant axis. These differences can be explained by differences in auditory sensitivity between the two species and the motor theory of speech perception. A vowel, which is pronounced by different speakers, has different acoustic properties. However, humans can perceive these speech sounds as the same vowel. The phenomenon of perceptual constancy in speech perception was studied in chimpanzees using natural vowels and a synthetic [o]- [a] continuum. The chimpanzees ignored the difference in the sex of the speakers and showed a capacity for vocal tract normalization.     

Endocranial shape changes during growth in chimpanzees and humans: A morphometric analysis of unique and shared aspects

Compared to our closest living and extinct relatives, humans have a large, specialized, and complex brain embedded in a uniquely shaped braincase. Here, we quantitatively compare endocranial shape changes during ontogeny in humans and chimpanzees. Identifying shared and unique aspects in developmental patterns of these two species can help us to understand brain evolution in the hominin lineage.Using CT scans of 58 humans and 60 chimpanzees varying in age from birth to adulthood, we generated virtual endocasts to measure and analyze 29 three-dimensional endocranial landmarks and several hundred semilandmarks on curves and the endocranial surface; these data were then analyzed using geometric morphometric methods.The ontogenetic shape trajectories are nonlinear for both species, which indicates several developmental phases. Endocranial shape is already distinct at birth and there is no overlap between the two species throughout ontogeny. While some aspects of the pattern of endocranial shape change are shared between humans and chimpanzees, the shape trajectories differ substantially directly after birth until the eruption of the deciduous dentition: in humans but not in chimpanzees, the parietal and cerebellar regions expand relatively (contributing to neurocranial globularity) and the cranial base flexes within the first postnatal year when brain growth rates are high. We show that the shape changes associated with this early “globularization phase” are unique to humans and do not occur in chimpanzees before or after birth.     

Telomere dynamics in HIV-1 infected and uninfected chimpanzees measured by an improved method based on high-resolution two-dimensional calibration of DNA sizes

We developed an improved method for accurately measuring telomere lengths based on two-dimensional calibration of DNA sizes combined with pulsed field electrophoresis and quantitative analysis of high-resolution gel images. This method was used to quantify the length of telomeres in longitudinal samples of peripheral blood mononuclear cells (PBMCs) from five chimpanzees infected with human immunodeficiency virus type 1 (HIV-1) and three uninfected animals, 14 to 27 years of age. The average length of the telomere restriction fragments (TRF) of infected and uninfected chimpanzees were 11.7 ± 0.25 kbp, and 11.6 ± 0.61 kbp, respectively, and were about 1 kbp and 3 kbp longer than those of human infants and 30 year old adults, respectively. There was a trend of a slight decrease (30–60 bp per year) in the TRF of two HIV infected chimpanzees over 30–35 months, while the TRF of one naive chimpanzee slightly increased over 20 months. Although the number of chimpanzees in this study is small and no statistically significant linear dependencies on time were observed, it appears that in chimpanzees, rates of shortening of the TRF are comparable or smaller than in adult humans and are not significantly affected by HIV-1 infection, which may be related to the inability of HIV-1 to cause disease in these animals.     

Quantification of the spatial strain distribution of scoliosis using a thin-plate spline method

The objective of this study was to quantify the three-dimensional spatial strain distribution of a scoliotic spine by nonhomogeneous transformation without using a statistically averaged reference spine. The shape of the scoliotic spine was determined from computed tomography images from a female patient with adolescent idiopathic scoliosis. The shape of the scoliotic spine was enclosed in a rectangular grid, and symmetrized using a thin-plate spline method according to the node positions of the grid. The node positions of the grid were determined by numerical optimization to satisfy symmetry. The obtained symmetric spinal shape was enclosed within a new rectangular grid and distorted back to the original scoliotic shape using a thin-plate spline method. The distorted grid was compared to the rectangular grid that surrounded the symmetrical spine. Cobb's angle was reduced from 35° in the scoliotic spine to 7° in the symmetrized spine, and the scoliotic shape was almost fully symmetrized. The scoliotic spine showed a complex Green–Lagrange strain distribution in three dimensions. The vertical and transverse compressive/tensile strains in the frontal plane were consistent with the major scoliotic deformation. The compressive, tensile and shear strains on the convex side of the apical vertebra were opposite to those on the concave side. These results indicate that the proposed method can be used to quantify the three-dimensional spatial strain distribution of a scoliotic spine, and may be useful in quantifying the deformity of scoliosis.     

The effects of linear perspective on relative size discrimination in chimpanzees (Pan troglodytes) and humans (Homo sapiens)

In this study, we tested the corridor illusion in three chimpanzees and five humans, applying a relative size discrimination task to assess pictorial depth perception using linear perspective. The subjects were required to choose the physically larger cylinder of two on a background containing drawn linear perspective cues. We manipulated both background and cylinder size in each trial. Our findings suggest that chimpanzees, like humans, exhibit the corridor illusion.     

Learning to use illumination gradients as an unambiguous cue to three dimensional shape

The luminance and colour gradients across an image are the result of complex interactions between object shape, material and illumination. Using such variations to infer object shape or surface colour is therefore a difficult problem for the visual system. We know that changes to the shape of an object can affect its perceived colour, and that shading gradients confer a sense of shape. Here we investigate if the visual system is able to effectively utilise these gradients as a cue to shape perception, even when additional cues are not available. We tested shape perception of a folded card object that contained illumination gradients in the form of shading and more subtle effects such as inter-reflections. Our results suggest that observers are able to use the gradients to make consistent shape judgements. In order to do this, observers must be given the opportunity to learn suitable assumptions about the lighting and scene. Using a variety of different training conditions, we demonstrate that learning can occur quickly and requires only coarse information. We also establish that learning does not deliver a trivial mapping between gradient and shape; rather learning leads to the acquisition of assumptions about lighting and scene parameters that subsequently allow for gradients to be used as a shape cue. The perceived shape is shown to be consistent for convex and concave versions of the object that exhibit very different shading, and also similar to that delivered by outline, a largely unrelated cue to shape. Overall our results indicate that, although gradients are less reliable than some other cues, the relationship between gradients and shape can be quickly assessed and the gradients therefore used effectively as a visual shape cue.     

Interaction sequences between chimpanzees and human visitors at the Zoo

Data were collected on the behavior and physical characteristics of 259 human visitors and 24 chimpanzees at Chester Zoo. The successive responses of humans and chimpanzees to each other's behavior were recorded, the resulting long sequence being referred to as an interaction sequence. There was no particular set of characteristics that distinguished interactors from noninteractors in either humans or chimpanzees, although there was some evidence that chimpanzees were particularly likely to respond to men carrying objects. Chimpanzee responses were random with respect to the previous human behavior, but human responses were significantly associated with the preceding chimpanzee behavior. In particular, chimpanzee sounds were likely to be followed by human sounds, and begging was likely to be followed by the offer of food. Interaction sequences varied in length, but 9% of chimpanzee-initiated sequences went as far as a ninth interaction. Sequences resulted in the chimpanzees being given food in 25% of human-initiated, but only 8% of chimpanzee-initiated sequences. The results are consistent with the interpretation that humans and chimpanzees are motivated to interact with one another and that the chimpanzees do this primarily to obtain food. © 1995 Wiley-Liss, Inc.     

Differences in breast shape preferences between plastic surgeons and patients seeking breast augmentation

There has been little discussion in the published literature regarding breast shape preferences. This study was conducted to ascertain previously undocumented differences in breast shape preferences between plastic surgeons and patients seeking breast augmentation, with respect to upper-pole contour. Sixty-six respondents, grouped into three cohort categories (plastic surgeons, breast augmentation patients, and lay people), were asked to evaluate a series of 12 nonptotic breast profiles representing a range of upper-pole contours. Five profiles exhibited convex upper-pole contours, five exhibited concave contours, and two exhibited upper poles with flat slopes. A five-point Likert-type scale was used to rate attractiveness, naturalness, how close the shape was to each respondent's personal ideal, and how close the shape was to what the respondent believed was our society's ideal. Statistical comparisons were made among the three cohorts. The plastic surgeon cohort (n = 11) rated concave upper-pole contours significantly higher than did the patient cohort (n = 13) for attractiveness, naturalness, and personal ideal (p < 0.01). For convex contours, the plastic surgeon cohort gave significantly lower scores than did the patient cohort (p < 0.01). The lay category (n = 42) demonstrated preferences intermediate between those of the other groups. There are no known studies in the literature documenting the breast shape preferences of plastic surgeons and their patients. This study suggests that plastic surgeons and patients seeking breast augmentation may have drastically different images in mind regarding what constitutes an attractive, natural, and ideal breast shape. These findings have potential implications for patient treatment and satisfaction.     

Subcellular curvature at the perimeter of micropatterned cells influences lamellipodial distribution and cell polarity

This paper employs substrates that are patterned with shapes having well-defined geometric cues to characterize the influence of curvature on the polarization of highly metastatic B16F10 rat melanoma cells. Substrates were patterned using microcontact printing to define adhesive islands of defined shape and size on a background that otherwise prevents cell adhesion. Cells adherent to these surfaces responded to local curvature at the perimeter of the adhesive islands; convex features promoted the assembly of lamellipodia and concave features promoted the assembly of stress filaments. Cells adherent to rectangular shapes displayed a polarized cytoskeleton that increased with the aspect ratio of the shapes. Shapes that combined local geometric cues, by way of concave or convex edges, with aspect ratio were used to understand the additive effects of shape on polarization. The dependence of cell polarity on shape was determined in the presence of small molecules that alter actomyosin contractility and revealed a stronger dependence on contractility for shapes having straight edges, in contrast to those having curved edges. This study demonstrates that the cytoskeleton modulates cell polarity in response to multiple geometric cues in the extracellular environment.     

At least at the level of inferior temporal cortex,the stereo correspondence problem is solved

Stereoscopic vision requires the correspondence problem to be solved, i.e., discarding "false" matches between images of the two eyes, while keeping correct ones. To advance our understanding of the underlying neuronal mechanisms, we compared single neuron responses to correlated and anticorrelated random dot stereograms (RDSs). Inferior temporal neurons, which respond selectively to disparity-defined three-dimensional shapes, showed robust selectivity for correlated RDSs portraying concave or convex surfaces, but unlike neurons in areas V1, MT/V5, and MST, were not selective for anticorrelated RDSs. These results show that the correspondence problem is solved at least in far extrastriate cortex, as it is in the monkey's perception.     

Comparison of auditory functions in the chimpanzee and human

Absolute thresholds for pure tones, loudness, frequency and intensity difference thresholds and the resonance of the external auditory meatus were measured in chimpanzees and compared with those in humans. Chimpanzees were more sensitive than humans to frequencies higher than 8 kHz but less sensitive to frequencies lower than 250 Hz and 2- to 4-kHz tones. Difference thresholds for frequency and intensity were greater in chimpanzees than in humans. The resonance of the external ear was about the same in the two species. The effects of differences in hearing between species upon speech perception are discussed.     

The geographic apportionment of mitochondrial genetic diversity in east African chimpanzees, Pan troglodytes schweinfurthii

This study is a geographically systematic genetic survey of the easternmost subspecies of chimpanzee, Pan troglodytes schweinfurthii. DNA was noninvasively collected in the form of shed hair from chimpanzees of known origin in Uganda, Rwanda, Tanzania, and Zaire. Two hundred sixty-two DNA sequences from hypervariable region 1 of which of the mitochondrial control region were generated. Eastern chimpanzees display levels of mitochondrial genetic variation which are low and which are similar to levels observed in humans (Homo sapiens). Also like humans, between 80% and 90% of the genetic variability within the eastern chimpanzees is apportioned within populations. Spatial autocorrelation analysis shows that genetic similarity between eastern chimpanzees decreases clinically with distance, in a pattern remarkably similar to one seen for humans separated by equivalent geographic distances. Eastern chimpanzee mismatch distributions (frequency distributions of pairwise genetic differences between individuals) are similar in shape to those for humans, implying similar population histories of recent demographic expansion. The overall pattern of genetic variability in eastern chimpanzees is consistent with the hypothesis that the subject has responded demographically to paleoclimatically driven changes in the distribution of eastern African forests during the recent Pleistocene.      

Apolipoprotein A-I of primates

Monkey apoA-I was isolated by ultracentrifugation or immunoprecipitation and analyzed by isoelectric focusing and two-dimensional polyacrylamide gel electrophoresis. The plasma apoA-I of 26 Old World monkeys (12 cynomolgus and 14 rhesus), 40 New World monkeys (8 cebus, 8 squirrel, 8 spider, 8 owl, and 8 marmosets), 6 prosimians (lemurs) and 10 apes (5 gibbons and 5 chimpanzees) were compared with each other as well as with human apoA-I. These analyses showed that monkey apoA-I contained one major and one to three minor (two basic and one acidic) isoproteins. The basic and acidic minor isoproteins differed by +2, +1, and -1 charges from the major apoA-I isoprotein designated apoA-I2. We have observed profound differences among the apoA-I electrophoretic patterns of the various primate species studied. The apparent isoelectric points of the major isoproteins of apoA-I of prosimians, Old World monkeys, New World monkeys, chimpanzees, gibbons, and humans were 5.70, 5.80, 5.35, 5.64, 5.42, and 5.64, respectively. The entire apoA-I isoprotein pattern of prosimians, Old World monkeys, chimpanzees, gibbons, and New World monkeys with respect to humans was shifted by approximately +1.5, +0.5, 0, -2.0, and -2.5 charges, respectively. The apoA-I synthesized by organ cultures of cynomolgus monkey intestine and liver overlaps on the two-dimensional system with the corresponding most basic minor plasma apoA-I isoprotein designated apoA-I2.(ABSTRACT TRUNCATED AT 250 WORDS)     

Morphological analyses and 3D modeling of the tongue musculature of the chimpanzee (Pan troglodytes)

Knowledge of the comparative anatomy of tongue musculature is crucial to the discussion of the origin and the evolution of speech because of the indispensable role played by this organ in speech. However, the tongue musculature of primates has rarely been studied. In a previous study, the author analyzed human tongue musculature and developed a 3D model of this organ [Takemoto, Journal of Speech, Language, and Hearing Research 44:95-107, 2001]. In this study, the tongue musculature of chimpanzees was examined using methods similar to those used for humans. Results showed that tongue musculature was topologically the same for both humans and chimpanzees. As in humans, the tongue musculature of chimpanzees consisted of inner and outer regions. The inner musculature was composed of serial "structural units," made up of two types of laminae whose fibers were perpendicular to the tongue surface. The outer musculature was a thin layer of fibers oriented parallel to the surface and superficial to the inner musculature. Although the tongue musculature of humans and chimpanzees is similar, the external shapes differ: the chimpanzee tongue is flat, whereas the human tongue is round. Applying the muscular hydrostat theory to the external shape of the tongue suggests that the primary actions of the chimpanzee tongue are protrusion and retrusion, whereas the human tongue can be deformed in the oral cavity with a high degree of freedom. It is hypothesized that the evolution of the external shape of the tongue is one of the factors that led to the development of human speech. The results of this study suggest that modeling based on muscular hydrostatic theory of the effects of changes in external tongue shape on articulatory movements should be included in discussions on the origin of speech.     

Visual preference by chimpanzees (Pan troglodytes) for photos of primates measured by a free choice-order task: implication for influence of social experience

With a free-choice task, visual preference was estimated in five adult chimpanzees (Pan troglodytes). The subjects were presented with digitized color photographs of various species of primates on a CRT screen. Their touching responses to the photographs were reinforced by food reward irrespective of which photographs they touched. The results revealed that all chimpanzees touched the photographs of humans significantly more than any other species, or phylogenetic families of primates. This tendency was consistent across different stimulus sets. The results suggest that the chimpanzees showed visual preference for the photographs of humans over those of their own species. The results also suggest that the degree of this visual preference was not in accordance with phylogenetic distance from the subjects' species, chimpanzees. The preference for humans was stronger in the case of the colored photographs than in monochromatic ones. All of the five chimpanzees had been in captivity for at least 16 years. They were reared by humans from just after their birth, or at least from 1.5 years old. Their preference might have developed through social experience, especially that during infanthood. Electronic Publication     

Perception of shape-from-motion in macaque monkeys and humans

Motion is one of the most efficient cues for shape perception. We conducted behavioral experiments to examine how monkeys perceive shapes defined by motion cues and whether they perceive them as humans do. We trained monkeys to perform a shape discrimination task in which shapes were defined by the motion of random dots. Effects of dot density and dot speed on the shape perception of monkeys were examined. Human subjects were also tested using the same paradigm and the test results were compared with those of monkeys. In both monkeys and humans, correct performance rates declined when density or speed of random dots was reduced. Both of them tended to confuse the same combinations of shapes frequently. These results suggest that monkeys and humans perceive shapes defined by motion cues in a similar manner and probably have common neural mechanisms to perceive them. Electronic Publication     

Similar numbers but different repertoires of olfactory receptor genes in humans and chimpanzees

Animals recognize their external world through the detection of tens of thousands of chemical odorants. Olfactory receptor (OR) genes encode proteins for detecting odorant molecules and form the largest multigene family in mammals. It is known that humans have fewer OR genes and a higher fraction of OR pseudogenes than mice or dogs. To investigate whether these features are human specific or common to all higher primates, we identified nearly complete sets of OR genes from the chimpanzee and macaque genomes and compared them with the human OR genes. In contrast to previous studies, here we show that the number of OR genes ( approximately 810) and the fraction of pseudogenes (51%) in chimpanzees are very similar to those in humans, though macaques have considerably fewer OR genes. The pseudogenization rates and the numbers of genes affected by positive selection are also similar between humans and chimpanzees. Moreover, the most recent common ancestor between humans and chimpanzees had a larger number of functional OR genes (>500) and a lower fraction of pseudogenes (41%) than its descendents, suggesting that the OR gene repertoires are in a phase of deterioration in both lineages. Interestingly, despite the close evolutionary relationship between the 2 species, approximately 25% of their functional gene repertoires are species specific due to massive gene losses. These findings suggest that the tempo of evolution of OR genes is similar between humans and chimpanzees, but the OR gene repertoires are quite different between them. This difference might be responsible for the species-specific ability of odor perception.     

How chimpanzees look at pictures: a comparative eye-tracking study

Surprisingly little is known about the eye movements of chimpanzees, despite the potential contribution of such knowledge to comparative cognition studies. Here, we present the first examination of eye tracking in chimpanzees. We recorded the eye movements of chimpanzees as they viewed naturalistic pictures containing a full-body image of a chimpanzee, a human or another mammal; results were compared with those from humans. We found a striking similarity in viewing patterns between the two species. Both chimpanzees and humans looked at the animal figures for longer than at the background and at the face region for longer than at other parts of the body. The face region was detected at first sight by both species when they were shown pictures of chimpanzees and of humans. However, the eye movements of chimpanzees also exhibited distinct differences from those of humans; the former shifted the fixation location more quickly and more broadly than the latter. In addition, the average duration of fixation on the face region was shorter in chimpanzees than in humans. Overall, our results clearly demonstrate the eye-movement strategies common to the two primate species and also suggest several notable differences manifested during the observation of pictures of scenes and body forms.