Northwestern Namibia Research Articles

Rizzo, Lorena: Gender and Colonialism. A History of Kaoko in North-Western Namibia, 1870s–1950s

Rizzo, Lorena: Gender and Colonialism. A History of Kaoko in North-Western Namibia, 1870s–1950s

Perceptions of emotion from facial expressions are not culturally universal: Evidence from a remote culture.

It is widely believed that certain emotions are universally recognized in facial expressions. Recent evidence indicates that Western perceptions (e.g., scowls as anger) depend on cues to U.S. emotion concepts embedded in experiments. Because such cues are standard features in methods used in cross-cultural experiments, we hypothesized that evidence of universality depends on this conceptual context. In our study, participants from the United States and the Himba ethnic group from the Keunene region of northwestern Namibia sorted images of posed facial expressions into piles by emotion type. Without cues to emotion concepts, Himba participants did not show the presumed "universal" pattern, whereas U.S. participants produced a pattern with presumed universal features. With cues to emotion concepts, participants in both cultures produced sorts that were closer to the presumed "universal" pattern, although substantial cultural variation persisted. Our findings indicate that perceptions of emotion are not universal, but depend on cultural and conceptual contexts.

<p class="Default">Euphorbia otjipembana subsp. okakoraensis (Euphorbiaceae), a new subspecies from the Kaokoveld, Namibia, with an amplified description of Euphorbia otjipembana

Euphorbia otjipembana was hitherto only known from the type locality within the Kaokoveld Centre of Endemism, northwestern Namibia. Subsequently several additional populations were discovered, allowing for an amplified description of the species and the recognition of two subspecies. Euphorbia otjipembana subsp. okakoraensis, here described as a new subspecies, is only known from a small area within the Kaokoveld Centre. Diagnostic characters for subsp. okakoraensis include a shrubby habit and medium (up to 1 m) height, 5–7-angled, scarcely constricted branches with two pairs of spines per node and single cymes comprising of three horizontally arranged cyathia. A key as well as a comparative table with diagnostic morphological characters to distinguish between the two subspecies of E. otjipembana is provided.

Development process of the vegetation on termite mounds in the Mopane woodland in north-western Namibia

Development process of the vegetation on termite mounds in the Mopane woodland in north-western Namibia

Gene flow in mongooses endemic to Namibia's granite inselbergs despite past climatic fluctuations and isolating landscape features

Past climatic fluctuations have had a significant impact on the patterns of genetic variation within taxa restricted to montane regions and forested biomes; however, little is known about whether equivalent processes have occurred in arid biomes. Northwestern Namibia's inselbergs provide a unique ecosystem in which to study the effects of major climatic events and geographical isolation on the genetic structuring of taxa in a subtropical arid biome. We investigated the phylogeographic structure of the black mongoose (Galerella nigrata), an inselberg habitat specialist endemic to this region, using mitochondrial DNA (mtDNA) haplotypes (cytochrome b, 1,089 base pairs) and nuclear microsatellite genotypes (15 loci) from 6 inselberg populations. Analyses of molecular variance and spatial analyses of molecular variance of the 14 mtDNA haplotypes identified 2 significant geographic barriers to the dispersal of black mongooses; these barriers occurred across the vast arid plains between Ruacana and Hobatere, and between Ohorongo and inselbergs to the south. The occurrence of mtDNA haplotypes that were restricted to specific populations also indicated some degree of isolation, likely resulting from limited gene flow and drift induced by the desertification of the landscape between inselbergs during the lead-up to the most recent glacial maxima. Despite this pattern of isolation, the widespread distribution of 1 mtDNA haplotype suggested that populations of black mongoose have, in general, been well connected in the past. Ongoing gene flow was further supported by Bayesian clustering of microsatellite genotypes, which showed 2 clusters, each spread across the mongoose's distribution, and a lack of significant differentiation between populations. In addition, a constant population size was indicated by a Bayesian skyline plot. These analyses suggested that inselbergs across the entire study area might have supported black mongoose populations during some or all of the most recent major climatic fluctuations, with periods of isolation during glacial maxima and reestablished connectivity during interglacial periods.

REVIEW OF MESOPROTEROZOIC MAGMATISM, SEDIMENTATION AND TERRANE AMALGAMATION IN SOUTHWESTERN AFRICA

Mesoproterozoic crustal evolution of southwestern Africa involved a complex interplay over 600 million years of subduction, plate-margin or intraplate sedimentation, volcanism and plutonism followed by terrane amalgamation, tectonism, collision, magmatism, metamorphism and final, late-stage isostatic rebound of high-grade terranes. Most terranes are underlain by ~2.0 Ga continental crust but the Areachap and Garies Terranes were juvenile Mesoproterozoic features with respective model ages of ~1.5 to ~1.3 Ga and ~1.25 Ga. Pre- and syntectonic metasediments in northwestern Namibia and in the Namaquan terranes are mid to late Mesoproterozoic in age. Volcanism or plutonism accompanied sedimentation in places. A southward younging of terrane accretion is apparent from about ~1.37 Ga in northwestern Namibia, to ~1.24 Ga(?) in the region of the central Damara Orogen, <1.33 Ga in the Konkiep Subprovince, the latter on the west-dipping Namaqua Front, ~1.2 Ga (O’okiepian episode) in the Kaaien Terrane, to between ~1.11 and ~1.07 Ga in the Bushmanland and Garies Terranes. Widespread intrusion of granite into the base of the crust accompanied collision in northwestern Namibia. Syntectonic granite magmatism was extensive and voluminous during O’okiepian collision in the Gordonia Subprovince. Thereafter, local intermittent magmatism and sedimentation continued in the Rehoboth and Konkiep Subprovinces and the Kaaien, Bushmanland and Garies Terranes. In most regions from the Rehoboth Subprovince to the Garies Terrane there was an ~1.1 Ga period of magmatism and/or metamorphism which Hanson et al. (2004, 2006) relate to plume activity. Redbed successions post-date the youngest magmatic rocks in the Rehoboth and Konkiep Subprovinces. The Bushmanland and Garies Terranes appear to have been subjected to intense deformation, recumbent folding and thrusting between ~1.11 and ~1.07 Ga. Open, upright folding thereafter in these two terranes was accompanied by intrusions of the Spektakel and Koperberg Suites and granulite-facies metamorphism between ~1.06 and ~1.02 Ga. Pegmatites mark the final magmatic event at about 1000 Ma. The high-grade rocks of the Gordonia Subprovince were juxtaposed against low-grade terranes to the north and south during isostatic rebound on major, late-stage, dextral shear zones at or near the margins of the subprovince. Cooling to 300 to 350°C had taken place by 850 to 800 Ma.

FERRUGINATED AND LEACHED LAPILLI TUFF AND TUFF IN THE VERBRANDE BERG FORMATION, ECCA GROUP, HUAB BASIN, NAMIBIA

Burnt Mountain is the name attached to a series of low, dark-coloured hills, dominantly composed of carbonaceous shale, siltstone, sandstone and various ferruginous rocks belonging to the Permian Verbrande Berg Formation, Ecca Group, Karoo Supergroup, in the Huab Basin, northwestern Namibia. At this site, which owes its name to the “burnt” appearance of the rocks, the Ecca Group rocks form a 150 m high mesa, capped with aeolian sandstone of the Cretaceous Twyfelfontein Formation, Etendeka Group. Reinvestigation of the outcrops at Burnt Mountain revealed that the exceptional 600 m-wide outcrop of the Verbrande Berg Formation at this site is the result of a north-south normal fault with a downthrow to the west. This fault forms one of a series of comparable north-south-striking structures in the Huab Basin that are linked to the opening of the proto-Atlantic Ocean. In the lower part of the Verbrande Berg Formation, where the carbonaceous shale is enriched in carbon, lenses of ferruginous fossiliferous carbonate rocks (FFC) with abundant plant fossils, as well as large (m-sized), flattened, ferruginous concretions are developed. Small concretions (cm-sized) as well as bedding-parallel segregations of ferric oxyhydrate minerals (largely hematite and goethite) are common in the FFC and are interpreted to be sulphide-derived. In the middle part of the Verbrande Berg Formation, a prominent unit (PU) of a medium-bedded, micro-crystalline, ferruginous and porous rock (FPR) is interbedded with the carbonaceous shale and sandstone. The FPR, which contains altered relicts of glass particles and possibly accretionary lapilli spheres, is interpreted to be the leached and ferruginated product of coarse-grained vitric lithic lapilli tuff and tuff, emplaced on an active swamp surface. The associated volcanic activity apparently was long-lived and culminated in the deposition of the PU. The ferrugination of the FPR is attributed to interaction of the nascent volcaniclastic rocks with acid bog water, augmented by oxidation products of early diagenetic sulphide that formed in the FPR on burial. Prolific development in places of Liesegang structures in the FPR is ascribed to fault-related fracturing and the infiltration of oxygenated meteoric water, prior to the intrusion of dolerite dykes that are here tentatively associated with the Etendeka volcanism. The positive identification of volcaniclastic rocks in the Verbrande Berg Formation in the Huab Basin corresponds to the occurrence of tuffs, at the same stratigraphic level, in comparable rocks in the Aranos Basin in southern Namibia as well as in the western parts of main Karoo Basin in South Africa. The FPR is the main source of the dark-coloured hematitic clasts (“clinker-like” rock) which contribute to the “burnt” appearance of the Burnt Mountain.

Species boundaries and possible hybridization between the black mongoose (Galerella nigrata) and the slender mongoose (Galerella sanguinea)

Major climatic oscillations since the mid-Miocene climatic optimum are known to have played a key role in promoting speciation events. In this study we use molecular data to elucidate the evolutionary history of Galerella nigrata and link its divergence to known major climatic events. A total of 51 samples from G. nigrata and 17 from Galerella sanguinea were used to provide the first molecular evidence that G. nigrata may be a species in its own right. Both mitochondrial cytochrome b and the nuclear ß-fibrinogen intron seven sequences of G. nigrata form distinct monophyletic clades, separate from its sister species G. sanguinea. We estimate the divergence of these two species to have occurred 3.85–4.27million years ago, coinciding with a period of the Plio-Pleistocene that was characterised by cooling global temperatures and strong aridity in southern Africa. However, evidence for potential hybridization between the two species was documented for ten individuals using phenotypic (pelage colouration) and/or molecular (nuclear and mtDNA sequences and microsatellite loci) data. There appeared to be a bias towards unidirectional hybridization with all potential hybrids showing mtDNA haplotypes from G. nigrata. We suggest that as the desert expanded across Namibia, G. sanguinea likely retreated with the savanna, leaving some mongooses stranded on the granite inselbergs of north-western Namibia. Subsequent adaptation of these mongooses to local conditions on granite inselbergs could have led to ecological speciation. Secondary contact zones would have been re-established with subsequent global warming events. It appears that the two species have not yet undergone complete reproductive isolation.

Christa Kilian-Hatz: Khwe Dictionary

Before an assessment of this dictionary is made, it is important to place the Khwe language in its historical and social context. Khwe dam (language of the Khwe), as its speakers would prefer to call it, is a Khoisan language belonging to the Southern African Central-Khoisan under the Khoe cluster (Güldemann and Vossen 2000). It is spoken in Northern Botswana and in the Western Capri-vi Strip of Namibia in the Kavango region. As the compiler correctly observes, there are about 10 000 Khwe-speaking people who live in the Caprivi Strip of North-Western Namibia, Angola, Botswana and Zambia, and at Schmidtsdrift, South Africa. As can be expected from a speech community such as the Khwe, who prefer living in small communities, there are dialects within the Khwe dam. In Botswana, the notable varieties are the Buga (Sand Khwe) and the ≤Ani (River Khwe), which exhibit discernable linguistic differences at the lexical and grammatical levels. However, linguists agree, as Kilian-Hatz also indicates, that the Khwe dam dialectal varieties are definitely related and mutually fairly intelligible (cf. Güldemann and Vossen 2000). As a language that has not been elaborately codified, it is difficult to speak about a standard Khwe dam form. Many other social and linguistic activities need to be carried out to resolve the question of standard Khwe dam (cf. WIMSA 2001).

P1-S1.22 HSV-2 prevalence across a pastoral landscape: transmission and transition among the Himba and Tjimba populations

BackgroundSexual partnerships take multiple forms among the Himba and Tjimba people living in Northwestern Namibia, including polygynous and monogamous marriage, and long- and short-term extra-marital partnerships. We hypothesised that HSV-2...

An ice grounding-line wedge from the Ghaub glaciation (635 Ma) on the distal foreslope of the Otavi carbonate platform, Namibia, and its bearing on the snowball Earth hypothesis

Our detailed examination of the Ghaub Formation (possibly 635 Ma) on the distal foreslope of the Otavi carbonate platform is part of a regional study of the Congo paleocontinental margin in northwestern Namibia. Detrital carbonates of the Ghaub Formation disconformably overlie the Franni-aus Member of the Ombaatjie Formation, a coarsening-upward stack of carbonate turbidites and oolite-clast debris-flow breccias interpreted to be a glacioeustatic falling-stand wedge. Within the main Ghaub Formation, carbonate diamictites are interleaved with mesoscale, laminated to cross-laminated (climbing rippled) grainstones and mudstones, and conglomeratic carbonates. Amalgamation of diamictite units is observed where interleaved facies (grainstones/mudstones) are laterally discontinuous due to reactivation of erosion, followed by renewed deposition. The diamictite package is progradational overall and 80 m thick on average. It is overlain by the 5–15-m-thick Bethanis Member, which is unique in its lateral continuity, composite fining-upward trend, and distinctive interbedding of turbidite grainstones, argillaceous siltstones, climbing-rippled mudstones, and meter-scale stromatolite dropstones. Dropstones are ubiquitous within the finer-grained (Ghaub) lithofacies, and their presence, along with the facies context for subglacial and near grounding-line deposition, indicates a glacigenic origin for the Ghaub Formation, despite its subtropical paleolatitude and distal foreslope setting. We infer a glacial maximum represented by the sub-Ghaub disconformity, followed by the main Ghaub interval when an ice grounding line on the distal foreslope experienced abrupt step backs and readvances of limited magnitude, terminated by the Bethanis episode of unusually widespread iceberg calving and slope instability. The Bethanis Member is overlain conformably by the Keilberg Member of the Maieberg Formation. Reconstruction of the foreslope places the Ghaub grounding-line wedge >1.3 km vertically below the rim of the platform, implying an enormous base-level change upon deglaciation, when the platform was drowned below wave base for a period far exceeding the time scale for isostatic adjustment. The magnitude of base-level change supports the pan-glacial hypothesis that dynamic (thick) ice sheets existed simultaneously on virtually all continents. The snowball hypothesis that the oceans were also covered by glacial ice (sea-glacier) provides a simple explanation for the main Ghaub-to-Bethanis transition—terminal deglaciation was triggered by collapse of the sea-glacier.

Tourism, Indigenous People, and the Challenge of Development: The Representations of Ovahimbas in Tourism Promotion and Community Perceptions Toward Tourism

In Namibia the tourism industry is increasingly used as a medium for economic and social development goals in the country. By involving local communities the benefits of tourism are expected to trickle down to a local level where the tourist activities actually take place. These challenges highlight the need to discuss the nature of tourism and community relations and perceptions. First, the article overviews the role and representations of local people, namely Ovahimbas (or Himbas), in Namibian tourism promotion. Secondly, the article aims to analyze how the role of tourism is seen by the local Ovahimba communities in north western Namibia. The former overview is based on the contemporary tourism brochures while the latter is studied by using community interviews. Based on the tourism promotion, the representations of Ovahimbas are dominated by female depictions referring to historically constructed primitive, exotic, and erotic objects for Western tourists to explore. The Ovahimbas are trapped to play an unchanged static culture referring to a past in order to satisfy the expectations of nonlocal visitors. According to the interviews the local practices of tourism were seen as highly beneficial, however, and tourism-related developments were perceived positively. On the other hand, the position that local people placed themselves in tourism was referring to the same passive role also represented in the tourism brochures. It is evident that tourism development has not yet contributed sufficiently to community empowerment, participation, and control over tourism activities, for example, which are named as strategic aims in the national tourism plans and community-based policy goals in Namibia.

Negative Impacts of Termite Mounds on the Vegetation in Mopane Savanna in Northwestern Namibia

Negative Impacts of Termite Mounds on the Vegetation in Mopane Savanna in Northwestern Namibia

Transposition of structures in the Neoproterozoic Kaoko Belt (NW Namibia) and their absolute timing

Three structural profiles across the Coastal Terrane, the Boundary Igneous Complex and the Orogen Core have been studied in the Kaoko Belt of northwestern Namibia. The oldest known Si fabric is inherited from an older tectono-metamorphic event. It occurs in the Coastal Terrane only and the extent of its reworking increases from south to north. The S1 foliation reactivates or folds Si fabric in the Coastal Terrane and appears as an early planar fabric in granitoids of the Boundary Igneous Complex and migmatites of the Orogen Core domain. Superimposed subvertical S2 fabric corresponds to axial plane cleavage of upright close to isoclinal folds and the extent of its development also increases from south to north. Active migration of partial melt during S2 development in the Orogen Core dates the onset of this deformation at ~550 Ma. Distribution of F2 fold axes and L2 stretching lineations suggests pure shear–dominated deformation associated with development of N–S trending S2 cleavage preserved in the central profile, followed by sinistral simple shear–dominated deformation on newly developed NW–SE trending pervasive cleavage in the northern part of the area. Such spatial variation in the deformation record is attributed to the irregular shape of the Congo Craton indenter that is reflected by heterogeneous development of the S2 cleavage front in the Coastal Terrane and the Boundary Igneous Complex. Common orientation of L1 and L2 stretching lineations and solid-state reworking on both S1 and S2 planes suggest single event of sinistral transpression since 550 Ma with strain partitioning into domains of oblique thrusting (reactivated S1) and transcurrent sinistral shearing (S2 and S3). Such succession of deformation structures suggests that major subvertical shear zones in the Kaoko Belt do not correspond to early crustal discontinuities, but rather reflect late strain localization during cooling.

SHRIMP zircon dating and Nd isotopic systematics of Palaeoproterozoic migmatitic orthogneisses in the Epupa Metamorphic Complex of northwestern Namibia

The Epupa Metamorphic Complex constitutes the southwestern margin of the Congo Craton and is exposed in a hilly to mountainous terrain of northwestern Namibia, bordering the Kunene River and extending into southern Angola. It consists predominantly of granitoid gneisses which are migmatized over large areas. This migmatization locally led to anatexis and produced crustal-melt granites such as the Otjitanda Granite. We have undertaken reconnaissance geochemical studies and single zircon U–Pb SHRIMP and Pb–Pb evaporation dating of rocks of the Epupa Complex. The granitoid gneisses, migmatites and anatectic melts are similar in composition and constitute a suite of metaluminous to peraluminous, calc-alkaline granitoids, predominantly with volcanic arc geochemical signatures. The zircon protolith ages for the orthogneisses range from 1861 ± 3 to 1758 ± 3 Ma. Anatexis in the migmatitic Epupa gneisses was dated from a melt patch at 1762 ± 4 Ma, and the anatectic Otjitanda Granite has a zircon age of 1757 ± 4 Ma. Migmatization and anatexis therefore occurred almost immediately after granitoid emplacement and date a widespread high-temperature Palaeoproterozoic event at ∼1760 Ma which has not been recorded elswhere in northern Namibia. The Nd isotopic systematics of all dated samples are surprisingly similar and suggest formation of the protolith from a source region that probably separated from the depleted mantle about 2.4–2.0 Ga ago. A major Archaean component in the source area is unlikely. Structural reworking of the Epupa gneisses during the transpressional Neoproterozoic to early Palaeozoic Kaoko orogeny led to partial or complete obliteration of the older structures and resulted in spectacular low- to high-grade shear and mylonite zones. This reworking did not affect the U–Pb isotopic system in the zircons but documents partial destruction of the Congo cratonic margin. The Epupa granitoid rocks formed during an event generally referred to in Africa as the Eburnian orogeny, but the nature and tectonic setting of the Congo craton of southwestern Africa during this time remain largely unknown.

Evidence for progressive Holocene aridification in southern Africa recorded in Namibian hyrax middens: Implications for African Monsoon dynamics and the ‘‘African Humid Period’’

Presented here are stable nitrogen isotope data from a rock hyrax ( Procavia capensis) middens from northwestern Namibia that record a series of rapid aridification events beginning at ca. 3800 cal yr BP, and which mark a progressive decrease in regional humidity across the Holocene. Strong correlations exist between this record and other terrestrial and marine archives from southern Africa, indicating that the observed pattern of climate change is regionally coherent. Combined, these data indicate hemispheric synchrony in tropical African climate change during the Holocene, with similar trends characterising the termination of the ‘African Humid Period’ (AHP) in both the northern and southern tropics. These findings run counter to the widely accepted model of direct low-latitude insolation forcing, which requires an anti-phase relationship to exist between the hemispheres. The combined dataset highlights: 1) the importance of forcing mechanisms influencing the high northern latitudes in effecting low-latitude climate change in Africa, and 2) the potential importance of solar forcing and variations in the Earth's geomagnetic shield in determining both long-term and rapid centennial-scale climate changes, identifying a possible mechanism for the variations marking the AHP termination in both the southern and northern tropics.

Remote but in contact with history and the world

Sauter et al. (1) begin with the premise that the Himba with whom they worked in Kaokoland, northwestern Namibia, lived in isolation “with no exposure to other cultural groups through media or personal contact.” The authors have not adequately situated their informants in a historical or anthropological context. Had they done so, they would have seen how unlikely it is that the people with whom they worked had “not been exposed to the affective signals of individuals from cultural groups other than their own” (1).

Geochemical character and petrogenesis of Pan-African Amspoort suite of the Boundary Igneous Complex in the Kaoko Belt (NW Namibia)

In the Kaoko Belt of northwestern Namibia, syn-tectonic granitoids of the Boundary Igneous Complex intruded a NNW–SSE trending suture between the Neoproterozoic Coastal Terrane and Archaean–Neoproterozoic Congo Craton-derived foreland. Typical representatives of this syn-collision igneous association are ca. 550 Ma old K-feldspar–phyric, Bt ± Cam granites–granodiorites of the Amspoort suite, with minor Cpx gabbro and rare two-pyroxene dolerite bodies. The scarce Opx–Cpx–Bt dolerites could come from a CHUR-like mantle source ( 87Sr/ 86Sr 550∼ 0.7045, ε 550 Nd∼ 0). The rest of the Amspoort suite is interpreted as a product of HT anatexis of a heterogeneous lower crust, built mainly by immature metapsammites rich in arc-derived detritus with minor metabasite and intermediate metaigneous bodies. The most likely source appears to be the anatectic Coastal Terrane gneisses. Yet, partial melting of so far little constrained Congo Craton cover, if formed by immature and youthful detritus unrelated to the basement, cannot be discounted. In any case, the rather primitive Sr–Nd isotopic compositions of the Amspoort suite apart from dolerites ( ε 550 Nd = − 3.4 to − 5.3, 87Sr/ 86Sr 550 = 0.7063–0.711), rule out any major role for the Congo Craton-basement derived material, which is in sharp contrast to other, more southerly Pan-African granitoid complexes of the Kaoko Belt.

A cross-cultural study of the representation of shape: Sensitivity to generalized cone dimensions

Many of the phenomena underlying shape recognition can be derived from an assumption that the representation of simple parts can be understood in terms of independent dimensions of generalized cones, e.g., whether the axis of a cylinder is straight or curved or whether the sides are parallel or nonparallel. What enables this sensitivity? One explanation is that the representations derive from our immersion in a manufactured world of simple objects, e.g., a cylinder and a funnel, where these dimensions can be readily discerned independent of other stimulus variations. An alternative explanation is that genetic coding and/or early experience with extended contours—a characteristic of all naturally varying visual worlds—would be sufficient to develop the appropriate representations. The Himba, a seminomadic people in a remote region of Northwestern Namibia with little exposure to regular, simple artifacts, were virtually identical to western observers in representing generalized-cone dimensions of simple shapes independently. Thus immersion in a world of simple, manufactured shapes is not required for the development of a representation that specifies these dimensions independently.

Representation of Shape in Individuals From a Culture With Minimal Exposure to Regular, Simple Artifacts: Sensitivity to Nonaccidental Versus Metric Properties

Many of the phenomena underlying shape recognition can be derived from the greater sensitivity to nonaccidental properties of an image (e.g., whether a contour is straight or curved), which are invariant to orientation in depth, than to the metric properties of an image (e.g., a contour's degree of curvature), which can vary with orientation. What enables this sensitivity? One explanation is that it derives from people's immersion in a manufactured world in which simple, regular shapes distinguished by nonaccidental properties abound (e.g., a can, a brick), and toddlers are encouraged to play with toy shape sorters. This report provides evidence against this explanation. The Himba, a seminomadic people living in a remote region of northwestern Namibia where there is little exposure to regular, simple artifacts, were virtually identical to Western observers in their greater sensitivity to nonaccidental properties than to metric properties of simple shapes.