Using verbal and blind-walking distance estimates to investigate the two visual systems hypothesis

Verbal estimates of egocentric distance are usually too short at distances greater than several meters, yet blindfolded walking to previously viewed targets can be surprisingly accurate. We present evidence from three experiments for the existence of two visual pathways with differentencodings of perceived egocentric distance. We found that (1) blind-walking estimates of egocentric distance are consistently more accurate than verbal reports; (2) an indoor versus outdoor environment selectively influences verbal reports; and (3) wearing prism lenses, which displace the visual field vertically, selectively influences the blind-walking estimates. We interpret these results in terms of the two visual systems hypothesis.     

Empirical equivalence and underdetermination

Jarrett Leplin in A Novel Defense of Scientific Realism (1997) argues that if the thesis of empirical equivalence is cogent, then the thesis of underdetermination cannot even get off the ground. Part of Leplin's argument rests on the claim that auxiliary hypotheses can be independently confirmed, thus enabling us to determine the epistemic worth of a theory. This, in turn, helps in determining about what we should be realists. Leplin's claims are demonstrated to be problematic. Leplin wants, inconsistently, to use only those auxiliary hypotheses which dovetail with confirmed theories. Finally, a detail of Leplin's argument is found wanting.     

Extensionality, underdetermination and indeterminacy

I am grateful to Burton Dreben, Warren Goldfarb, Don Gustafson, Jim Higginbotham, Jerrold Katz, Joe Levine, Ted Morris, Nick Pappas, Hilary Putnam, Georges Rey and Bob Richardson for helpful discussions and comments on the issues discussed in this paper. Also I thank an anonymous reviewer for Erkenntnis for helpful comments.     

视觉注意捕获的快速脱离假说与信号抑制假说

快速脱离假说和信号抑制假说都是将传统的自下而上捕获和自上而下控制结合起来的混合模式假说。快速脱离假说认为突显干扰物总能在第一时间自下而上地捕获注意, 当突显干扰物与任务要求不符时, 注意会迅速脱离该位置。信号抑制假说认为突显干扰物都会产生“注意我”的信号, 当突显干扰物与任务要求不符时, 该信号会被自上而下地抑制以阻止注意捕获发生。前者相关的研究多采用空间线索提示范式和眼动脱离范式, 实验中被试采取独子探测策略, 而后者相关的研究多采用额外单例范式的变式, 实验中被试采取特征探测策略。未来研究应采用不同的刺激类型和实验方法进一步为两个假说提供证据支持, 同时要关注奖赏、训练等因素对“捕获-脱离”和“信号-抑制”的影响。     

Realism and the underdetermination of theory

The main theme is that theorizing serves empirical prediction. This is used as the core of a counter to contemporary anti-realist arguments. Different versions of the thesis that data underdetermines theory are identified and it is shown that none which are acceptable differentiates between theory selection and prediction. Criteria sufficient for the former are included amongst those necessary for the latter; and obviously go beyond mere compatibility with data.Special attention is given to causal process theories. It is argued that the only empirically equivalent alternatives which can be constructed to any theory of this kind must be parasitic on that theory; so a choice for the original theory can not be avoided. Once this is established, a positive case for taking a realist position can be developed.     

Recurrent transient underdetermination and the glass half full

Kyle Stanford’s arguments against scientific realism are assessed, with a focus on the underdetermination of theory by evidence. I argue that discussions of underdetermination have neglected a possible symmetry which may ameliorate the situation.

The demand for contrastive explanations

Philosophical Studies - A “contrastive explanation” explains not only why some event A occurred, but why A occurred as opposed to some alternative event B. Some philosophers argue that...     

Unawareness of visual and sensorimotor defects: A hypothesis

A theory is proposed to account for unawareness of blindness, hemianopsia, and hemiplegia, and for phantom limb after amputation. It is assumed that interruption of a sensory pathway at any level--from peripheral nerve to primary sensory cortex--is not associated with any immediate sensory experience that uniquely specifies the defect. Instead the sensory loss must be discovered by a process of self-observation and inference. Discovery is easy for defects that create major functional disability, such as total blindness. Hence unawareness of total blindness occurs only in association with severe intellectual impairment, precluding the required self-observation and inference. In contrast, hemianopsia is difficult to discover because several mechanisms automatically compensate the defect effectively. Thus unawareness of hemianopsia is common, even in intellectually normal individuals. Insensate fields are often the source of suggested (false) percepts, because no information from such a field specifies the absence of a sensory stimulus. The most powerful source of suggestion is sensory activity in uninvolved portions of the affected sensory field. Thus hemianopsics may perceive complete geometric forms when only incomplete forms are shown and the missing portion falls in the hemianopsic fields. Such perceptual completion also occurs in hemianesthetic hemiplegics, creating the illusion that there are normally functioning limbs on the affected side. This perceptual completion increases the difficulty of discovery of hemianesthetic hemiplegia, but the disability is still sufficiently obvious that some additional cognitive impairment is invariably present in patients with lasting unawareness of hemiplegia. Phantom limb after amputation is the product of perceptual completion without associated cognitive impairment. The patient with phantom limb is thus aware of the illusory quality of his phantom. Some insight into the neural basis of perceptual completion and of unawareness of sensory loss may derive from considering sensory systems and associative cortex as parallel-distributed processing mechanisms.     

Non-empirical theoretical virtues and the argument from underdetermination

The antirealist argument from the underdetermination of theories by data relies on the premise that the empirical content of a theory is the only determinant of its belief-worthiness (premise NN). Several authors have claimed that the antirealist cannot endorse NN, on pain of internal inconsistency. I concede this point. Nevertheless, this refutation of the underdetermination argument fails because there are weaker substitutes for NN that will serve just as well as a premise to the argument. On the other hand, antirealists have not made a convincing casefor NN (or its weaker substitutes) either. In particular, I criticize van Fraassen's recent claim that all ampliative rules in epistemology must be rejected on the grounds that they lead to incoherence. The status of the underdetermination argument remains unsettled.     

Pure optic ataxia and visual hemiagnosia – extending the dual visual hypothesis

Goodale and Milner's two visual system hypothesis is an influential model for the understanding of the primate visual system. Lesions of either the ventral (occipito‐temporal) or the dorsal (occipito‐parietal) stream produce distinct and dissociated syndromes in humans: visual agnosia is typical for ventral damage, whereas optic ataxia (OA) for dorsal damage. We studied the case of a 59‐year‐old left‐handed woman with a circumscribed lesion around the left posterior occipital sulcus, extending to the underlying white matter. Initially, she presented with a central visual field OA, which regressed to an OA to the right visual hemifield during the 3 months observation period. In addition, tachistoscopic experiments showed visual hemiagnosia to the right visual hemifield. In line with the findings of the neuropsychological experiments, the analysis of the structural MR data by means of a trackwise hodologic probabilistic approach revealed damage to the left superior longitudinal fasciculus and to the left inferior longitudinal fasciculus, indicating an impairment of both the dorsal and the ventral stream. The combination of OA and visual hemiagnosia in the same patient has never been previously described. The present case study thus provides further insights for the understanding of visual processing.     

Effects of two levels of stimulus complexity upon hypothesis sampling systems among second and sixth grade children

Groups of second and sixth grade children each solved a series of discrimination-learning problems involving four and eight dimensions that contained blanktrial probes for the S′s hypothesis (H). There were significant effects of grade level on three dependent measures (learning, generating consistent H patterns, sampling locally consistent Hs). Main effects of stimulus complexity were significant on five measures (the three above, rejecting disconfirmed Hs, maintaining confirmed Hs). There were no interactions involving any of these measures. The hypothesis sampling system (Sy) observed in each problem was also determined. Among sixth grade Ss this measure was unaffected by stimulus complexity level. Second grade Ss generated logically structured Sys in 65% of four-dimensional, but only 30% of eight-dimensional problems. They generated stereotyped behaviors or unsystematic sequences of Hs in 70% of eight-dimensional, but only about 35% of four-dimensional problems. Detailed analyses revealed that among second grade Ss good information processors (in terms of four component processes above) usually imposed a logical structure on four-dimensional, but generated unsystematic sequences of Hs in many of eight-dimensional problems. Poor processors generated stereotyped behaviors in both four- and eight-dimensional problems.     

The interaction of postural systems in visual orientation

Visual orientation judgments were made during right head tilt, left body tilt, and left trunk tilt, each of 30 deg. In these postures the otolith, neck, and trunk systems are stimulated in pairs. The hypothesis that the visual vertical during trunk tilt is equal to the algebraic sum ofthose in the same direction ofbody tilt and the opposite head tilt was tested and accepted. This result demonstrates the interaction of these postural systems in visual orientation, and complements the confirmation of the same hypothesis for the visual aftereffect following prolonged tilt.     

Trumping and contrastive causation

Jonathan Schaffer introduced a new type of causal structure called ‘trumping’. According to Schaffer, trumping is a species of causal preemption. Both Schaffer and I have argued that causation has a contrastive structure. In this paper, I analyze the structure of trumping cases from the perspective of contrastive causation, and argue that the case is much more complex than it first appears. Nonetheless, there is little reason to regard trumping as a species of causal preemption.     

Developmental dyslexia: the visual attention span deficit hypothesis

The visual attention (VA) span is defined as the amount of distinct visual elements which can be processed in parallel in a multi-element array. Both recent empirical data and theoretical accounts suggest that a VA span deficit might contribute to developmental dyslexia, independently of a phonological disorder. In this study, this hypothesis was assessed in two large samples of French and British dyslexic children whose performance was compared to that of chronological-age matched control children. Results of the French study show that the VA span capacities account for a substantial amount of unique variance in reading, as do phonological skills. The British study replicates this finding and further reveals that the contribution of the VA span to reading performance remains even after controlling IQ, verbal fluency, vocabulary and single letter identification skills, in addition to phoneme awareness. In both studies, most dyslexic children exhibit a selective phonological or VA span disorder. Overall, these findings support a multi-factorial view of developmental dyslexia. In many cases, developmental reading disorders do not seem to be due to phonological disorders. We propose that a VA span deficit is a likely alternative underlying cognitive deficit in dyslexia.     

The content, consequence and likeness approaches to verisimilitude: compatibility, trivialization, and underdetermination

Theories of verisimilitude have routinely been classified into two rival camps—the content approach and the likeness approach—and these appear to be motivated by very different sets of data and principles. The question thus naturally arises as to whether these approaches can be fruitfully combined. Recently Zwart and Franssen (Synthese 158(1):75–92, 2007) have offered precise analyses of the content and likeness approaches, and shown that given these analyses any attempt to meld content and likeness orderings violates some basic desiderata. Unfortunately their characterizations of the approaches do not embrace the paradigm examples of those approaches. I offer somewhat different characterizations of these two approaches, as well as of the consequence approach (Schurz and Weingartner (Synthese 172(3):415–436, 2010) which happily embrace their respective paradigms. Finally I prove that the three approaches are indeed compatible, but only just, and that the cost of combining them is too high. Any account which combines the strictures of what I call the strong likeness approach with the demands of either the content or the consequence approach suffers from precisely the same defect as Popper’s—namely, it entails the trivialization of truthlikeness. The downside of eschewing the strong likeness constraints and embracing the content constraints alone is the underdetermination of the concept of truthlikeness.