Animal detection in natural scenes: critical features revisited

S. J. Thorpe, D. Fize, and C. Marlot (1996) showed how rapidly observers can detect animals in images of natural scenes, but it is still unclear which image features support this rapid detection. A. B. Torralba and A. Oliva (2003) suggested that a simple image statistic based on the power spectrum allows the absence or presence of objects in natural scenes to be predicted. We tested whether human observers make use of power spectral differences between image categories when detecting animals in natural scenes. In Experiments 1 and 2 we found performance to be essentially independent of the power spectrum. Computational analysis revealed that the ease of classification correlates with the proposed spectral cue without being caused by it. This result is consistent with the hypothesis that in commercial stock photo databases a majority of animal images are pre-segmented from the background by the photographers and this pre-segmentation causes the power spectral differences between image categories and may, furthermore, help rapid animal detection. Data from a third experiment are consistent with this hypothesis. Together, our results make it exceedingly unlikely that human observers make use of power spectral differences between animal- and no-animal images during rapid animal detection. In addition, our results point to potential confounds in the commercially available "natural image" databases whose statistics may be less natural than commonly presumed.

Texture and object motion in slant discrimination: failure of reliability-based weighting of cues may be evidence for strong fusion

Different types of texture produce differences in slant-discrimination performance (P. Rosas, F. A. Wichmann, & J. Wagemans, 2004). Under the assumption that the visual system is sensitive to the reliability of different depth cues (M. O. Ernst & M. S. Banks, 2002; L. T. Maloney & M. S. Landy, 1989), it follows that the texture type should affect the influence of the texture cue in depth-cue combination. We tested this prediction by combining different texture types with object motion in a slant-discrimination task in two experiments. First, we used consistent cues to observe whether our subjects behaved as linearly combining independent estimates from texture and motion in a statistical optimal fashion (M. O. Ernst & M. S. Banks, 2002). Only 4% of our results were consistent with such an optimal combination of uncorrelated estimates, whereas about 46% of the data were consistent with an optimal combination of correlated estimates from cues. Second, we measured the weights for the texture and motion cues using perturbation analysis. The results showed a large influence of the motion cue and an increasing weight for the texture cue for larger slants. However, in general, the texture weights did not follow the reliability of the textures. Finally, we fitted the correlation coefficients of estimates individually for each texture, motion condition, and observer. This allows us to fit our data from both experiments to an optimal cue combination model with correlated estimates, but inspection of the fitted parameters shows no clear, psychophysically interpretable pattern. Furthermore, the fitted motion thresholds as a function of texture type are correlated with the slant thresholds as a function of texture type. One interpretation of such a finding is a strong coupling of cues.

Perceptual-motor adaptations in a synchronization task: The joint effects of frequency and motion coherence manipulations

Two experiments were conducted to examine the human ability to adapt to a perturbation in a synchronization task. Five experimental signal conditions were tested using random-dot kinematograms, representing four conditions with different coherence levels (100%, 50%, 30% and 10%) and one target-alone condition. Within one trial, increasing or decreasing the frequency of the sinusoidally moving signal dots abruptly in the midst of each trial provoked a perturbation. The first experiment was aimed to clarify the process of adaptation to the new frequency situation. The second experiment explored the role of visual feedback about the arm's position on the participants' ability to adapt after the perturbation had occurred. The results clearly demonstrated that the synchronization performance gradually declined in function of the increasing number of randomly moving noise dots. In the 50% coherence condition, the participants were not or only partially able to adjust their arm movements to the new frequency situation. In addition, the provision of enhanced visual feedback about the arm's failed to improve one's adaptive ability. In general, these findings provided evidence for the important role of perceptual constraints on perception-action coupling in this type of synchronization task.

The influence of motion coherence manipulations on the synchronization level of a perception–action task

The present experiment was conducted to examine the integration of the motion coherence paradigm in a synchronization task. Random-dot kinematograms were used to generate a pattern of oscillating dots representing four different coherence levels (10%, 30%, 50% and 100%) and one target-alone condition. The participants had to synchronize their arm with the coherently moving dots according to two different synchronization modes (in-phase and anti-phase). The results revealed a substantial performance decline when the target/noise ratio dropped under the critical threshold situated around the 30% coherence level, albeit independent of the synchronization mode. In general, these findings highlighted the impact of the perception of motion based on the level of motion coherence in the visual signal on the synchronization behavior in a perception-action setting.

Texture and haptic cues in slant discrimination: reliability-based cue weighting without statistically optimal cue combination

A number of models of depth-cue combination suggest that the final depth percept results from a weighted average of independent depth estimates based on the different cues available. The weight of each cue in such an average is thought to depend on the reliability of each cue. In principle, such a depth estimation could be statistically optimal in the sense of producing the minimum-variance unbiased estimator that can be constructed from the available information. Here we test such models by using visual and haptic depth information. Different texture types produce differences in slant-discrimination performance, thus providing a means for testing a reliability-sensitive cue-combination model with texture as one of the cues to slant. Our results show that the weights for the cues were generally sensitive to their reliability but fell short of statistically optimal combination--we find reliability-based reweighting but not statistically optimal cue combination.

Some observations on the effects of slant and texture type on slant-from-texture

We measure the performance of five subjects in a two-alternative-forced-choice slant-discrimination task for differently textured planes. As textures we used uniform lattices, randomly displaced lattices, circles (polka dots), Voronoi tessellations, plaids, 1/f noise, "coherent" noise and a leopard skin-like texture. Our results show: (1) Improving performance with larger slants for all textures, (2) and some cases of "non-symmetrical" performance around a particular orientation. (3) For orientations sufficiently slanted, the different textures do not elicit major differences in performance, (4) while for orientations closer to the vertical plane there are marked differences among them. (5) These differences allow a rank-order of textures to be formed according to their "helpfulness"--that is, how easy the discrimination task is when a particular texture is mapped on the plane. Polka dots tend to allow the best slant discrimination performance, noise patterns the worst. Two additional experiments were conducted to test the generality of the obtained rank-order. First, the tilt of the planes was rotated by 90 degrees. Second, the task was changed to a slant report task via probe adjustment. The results of both control experiments confirmed the texture rank-order previously obtained. We then test a number of spatial-frequency-based slant-from-texture models and discuss their shortcomings in explaining our rank-order. Finally, we comment on the importance of these results for depth-perception research in general, and in particular the implications our results have for studies of cue combination (sensor fusion) using texture as one of the cues involved.

Effects of infantile thymectomy on ovarian functions and gonadotrophin-induced ovulation in prepubertal mice: role of thymulin

The effects of thymectomy performed on 10-day-old (Tx-10) mice on spontaneous puberty and the ovulatory response induced by gonadotrophin treatment were analysed, together with the effects of thymulin replacement from 10 days of age. Infantile thymectomy induced a delay of puberty, a decrease in serum 17beta-oestradiol concentration and a reduced total number of follicles. Injection of thymulin (12 ng/g body weight) to Tx-10 mice resulted in an earlier onset of puberty, a decrease in the weights of ovaries and uterus, and an increase in serum 17beta-oestradiol concentrations. In control and Tx-10 mice, treatment with pregnant mare serum gonadotrophin (PMSG) (5 IU) at 25 days of age resulted in ovulation and the numbers of ova shed by ovulating animals were similar. When the animals were injected with 1 IU PMSG ovulation did not occur. In Tx-10 mice, both 1 and 5 IU PMSG increased the number of follicles to values similar to those observed in the controls. In Tx-10 mice the sequential injection of PMSG (1 IU) and human chorionic gonadotrophin (hCG) (3 IU) resulted in ovulation, but the number of ova shed was lower than in controls. When these animals were injected daily with thymulin, an increase in the number of ova shed and serum 17beta-oestradiol concentrations was observed. The uterine weight of Tx-10 mice was always significantly reduced in response to gonadotrophin treatment. Thymulin injection in PMSG-hCG-treated Tx-10 mice provoked a significant increase in uterine weight. The results suggest that the presence of the thymus after the neonatal period is necessary to normal ovarian development and function. The increase in gonadotrophin-induced ovarian response produced by thymulin replacement indicates that this peptide has a role in this process as one of the connecting signals between thymus and ovaries.

Effects of thymulin on spontaneous puberty and gonadotrophin-induced ovulation in prepubertal normal and hypothymic mice

The effects of thymulin administration beginning on days 19 or 24 of age on spontaneous puberty and gonadotrophin-induced ovulation were analysed in female normal and hypothymic mice. In normal and hypothymic mice, the daily administration of thymulin at 24 days of age resulted in a delay in the age of vaginal opening, with an increase in serum progesterone levels. Normal mice treated with 200 ng thymulin beginning on day 19 of age and injected with pregnant mare serum gonadotrophin (PMSG) 24 h later had an increase in ovulation rate, number of ova shed and weight of the ovaries. None of the hypothymic mice treated with thymulin on day 19 and PMSG on day 20 ovulated. PMSG treatment on day 25 induced ovulation in hypothymic mice. When these animals were injected previously with 200 ng thymulin, the number of ova shed by ovulating animals was lower than in PMSG-treated animals. Administration of thymulin and sequential injection of PMSG and human chorionic gonadotrophin 54 h later resulted in an increase in ovulatory response in comparison with those receiving only PMSG. The results suggest that thymulin plays a role in the regulation of spontaneous puberty through its effects on adrenal and ovarian endocrine functions. The increase in the ovarian PMSG response-treated animals, previously given thymulin, showed that this thymic hormone participates in the regulation of gonadotrophin secretion mechanisms and seems to be dose- and age-dependent. In hypothymic mice, neuroendocrine mechanisms regulating puberty are different from those of normal mice.

Different effects of unilateral and bilateral lesions of the dorsal raphe nucleus on puberty and first ovulation

The effects of unilateral and bilateral electrolytic lesions of the dorsal raphe nuclei (DRN) of 30-day-old rats, on the spontaneous and induced ovulation, were analyzed. The bilateral lesion and the lesion on the right side of the DRN delayed the age of first vaginal estrous. None of the animals with bilateral lesion on the DRN ovulated on the day of first estrous (0/8 vs. 12/15, p < 0.05). The ovulation rate in animals with unilateral lesion on the DRN was similar to sham-operated animals, but the number of ova shed by ovulating animals increased in the ovary ipsilateral to the lesion (lesion on right DRN, right ovary: 6.5 +/- 0.5 vs. 4.5 +/- 0.4; lesion on left DRN, left ovary: 6.4 +/- 0.3 vs. 4.2 +/- 0.4, p < 0.05). By the injection of human chorionic gonadotropin, ovulation was restored in rats with a bilateral lesion on the DRN (3/5 vs. 0/8, p < 0.05). The present results suggest that serotoninergic input to the hypothalamus, arising from the DRN, exerts a facilitatory influences on the control of luteinizing hormone release. To explain the increase in the number of ova shed by the left and right ovary, observed in rats with an ipsilateral lesion, we suggest the existence of a neural connection between the DRN and the ovary.

[Efficiency of an ELISA using complete and delipidated protein extract from Mycobacterium tuberculosis H37Rv strain as a serological test for ruling out pulmonary tuberculosis]

We present the results of an enzyme-linked immunosorbent assay that detects serum antibodies to M. tuberculosis antigens. The patients sera were tested with two different antigens, one a M. tuberculosis H37Rv culture filtrate protein extract precipitated with ammonium sulfate (CFPE), and the second, a delipidized CFPE (CFPE-d). The results obtained with 52 clearly defined TBP patients was 0.50 +/- 0.16 (CFPE) and 0.38 +/- 0.11 (CFPE-d). We also tested 165 sera from patients hospitalized at the INER with a diagnosis of non-tuberculous pulmonary disease. In this patients the assay revealed 153 negative sera (CFPE = 0.053 +/- 0.01; CFPE-d 0 0.050 +/- 0.004) and 12 positive sera. Nine of these patients (CFPE = 0.38 +/- 0.08; CFPE-d = 0.32 +/- 0.09) had mycobacterias and the results of the remaining three were considered as false positive. TBP was excluded in all the 153 negative patients. The elimination of lipids in the CFPE did not alter the assay since the differences between CFPE and CFPE-d did not reach statistical significance. In non-tuberculous individuals the reactivity with mycobacterial lipids was poor and didn't induce false positive results. The assay we report can be useful in those patients with pulmonary disease where TBP has to be considered.

Neuropsychological assessment in illiterates. II. Language and praxic abilities

A basic neuropsychological examination of language and praxic abilities was administered to extreme educational groups (100 illiterates and 100 professionals). Subjects were matched according to sex and age (16-25, 26-35, 36-45, 46-55, and 56-65). The following tasks were included: language comprehension, phonological discrimination, naming (objects, figures, and body parts), repetition of words, verbal fluency, calculation, buccofacial and ideomotor praxis, finger alternating movements, meaningless movements, cancellation task, coordinated movements with both hands, and motor impersistence tasks. All the differences between the two educational groups were statistically significant. Two of the eight language tests (phonological discrimination and naming figures) and three of the seven praxic tests (buccofacial praxis, coordinated movements, and cancellation task) showed differences between age groups with a better performance in the younger groups. Calculation tasks and ideomotor praxis showed differences between sexes with a better performance in males. Influence of educational factors in performing routine neuropsychological tests is analyzed.

Neuropsychological assessment in illiterates: visuospatial and memory abilities

A basic neuropsychological battery of visuospatial and memory abilities was administered to extreme educational groups (illiterates and professionals). Subjects were matched according to sex and age. The following visuospatial tasks were included: figure copy (cube, house, and Rey-Osterrieth complex figure), telling time, recognition of superimposed figures, recognition of a map, and drawing of the plan of the room. The following memory tasks were used: basic information, digit retention (forward and backward), memory curve, delayed verbal recall, sentence repetition, logical memory, delayed logical memory, immediate recall of the Rey-Osterrieth complex figure, immediate reproduction of a cube, visuospatial memory, and sequential memory. In visuospatial tasks all differences between the two groups were statistically significant. Five of the seven visuospatial tasks (all but telling time and recognition of superimposed figures) showed differences between age groups with a better performance found in the younger groups and four of the tasks (cube, house, Rey-Osterrith complex figure copying, and telling time) were significant between sexes with a better performance in men. In memory tasks, with the exception of the immediate memory of sentences, all tasks showed statistically significant differences between educational groups. Eight of the 13 memory tasks (digits forward and backward, delayed memory of words, immediate and delayed logical memory, Rey-Osterrieth immediate memory, cube immediate memory, and sequential memory) showed significant differences for age while 4 of the tasks (digits backward, memory curve, Rey-Osterrieth immediate memory, and cube immediate memory) were significant for sex. Results are analyzed with regard to current theories in cognitive psychology and anthropology. Emphasis is placed on the finding that cognitive skills usually examined by neuropsychological tests represent learned and highly trained abilities.