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T A Nazir

Publications and source records attributed to T A Nazir.

11 recordsLinked to original sources
PubMed2001

From "logographic" to normal reading: the case of a deaf beginning reader.

Visual word recognition of a profoundly deaf girl (AH) with developmental reading disorders was explored using an experimental technique that measures performance as a function of eye fixation within a word. AH's fixation-dependent word recognition profile revealed that she was inferring the identity of words using a "logographic" reading strategy (i. e., using salient visual features). Following this observation a special training program that enhances the understanding of grapheme-phoneme relations was applied. After few months of training, AH's reading skills improved, while her fixation-dependent performance changed to become like that of normal readers. We discuss the impact of our technique for the early diagnosis of reading impairments.

Child, Preschool↗
PubMed2001

Eye movement control in reading unspaced text: the case of the Japanese script.

The present study examines the landing-site distributions of the eyes during natural reading of Japanese script: a script that mixes three different writing systems (Kanji, Hiragana, and Katakana) and that misses regular spacing between words. The results show a clear preference of the eyes to land at the beginning rather than the center of the word. In addition, it was found that the eyes land on Kanji characters more frequently than on Hiragana or Katakana characters. Further analysis for two- and three-character words indicated that the eye's landing-site distribution differs depending on type of the characters in the word: the eyes prefer to land at the word beginning only when the initial character of the word is a Kanji character. For pure Hiragana words, the proportion of initial fixations did not differ between character positions. Thus, as already indicated by Kambe (National Institute of Japanese Language Report 85 (1986) 29), the visual distinctiveness of the three Japanese scripts plays a role in guiding eye movements in reading Japanese.

Analysis of Variance↗
PubMed2000

Developing normal reading skills: aspects of the visual processes underlying word recognition.

Visual word recognition performance of first graders (mean age: 6.6 years) through fifth graders (mean age: 10.8 years) was investigated using an experimental technique that is known to elicit the "viewing position effect" in skilled readers. The results showed that this effect, which consists of a systematic variation of performance as a function of fixation position within words, emerged early at the end of the 1st year of reading instruction. Visual field asymmetries in recognizing individual letters in words were also observed starting from first grade. Effects of word familiarity were obtained as early as in second grade. In contrast to skilled readers, children showed a marked word-length effect, which persisted through the first 5 years of instruction. No other qualitative differences between beginning and skilled readers were apparent. Hence, the basics of reading skills, as measured by the present technique, seem to be attained very early during acquisition. Further experience mainly reduces the time a reader needs to extract visual information from print.

Attention↗
PubMed1999

Lateral masking: limitations of the feature interaction account.

Recognition performance for a target letter embedded in a string of characters is worse than that for targets presented in isolation. This lateral masking (LM) effect is known to depend on target eccentricity and spacing between target and flankers (Bouma, 1970), indicating that LM arises in early visual processing due to interactions among visual features. The feature interaction account would predict that flankers consisting of similar features produce similar LM effects and that differences in LM produced by different types of flanker diminish with increasing target eccentricity and decreasing spacing. However, in a series of six experiments, this prediction was shown not to be true. Flankers that did not access a higher level code (e.g., pseudoletters or rotated letters) produced more LM than standard letter flankers. Moreover, effects of different flanker types were most pronounced for medium target eccentricities and medium spacings for which recognition performance scores ranged between 40% and 60%.

Adult↗
PubMed1998

Letter legibility and visual word recognition.

Word recognition performance varies systematically as a function of where the eyes fixate in the word. Performance is maximal with the eye slightly left of the center of the word and decreases drastically to both sides of this optimal viewing position. While manipulations of lexical factors have only marginal effects on this phenomenon, previous studies have pointed to a relation between the viewing position effect (VPE) and letter legibility: When letter legibility drops, the VPE becomes more exaggerated. To further investigate this phenomenon, we improved letter legibility by magnifying letter size in a way that was proportional to the distance from fixation (e.g., TABLE). Contrary to what would be expected if the VPE were due to limits of acuity, improving the legibility of letters has only a restricted influence on performance. In particular, for long words, a strong VPE remains even when letter legibility is equalized across eccentricities. The failure to neutralize the VPE is interpreted in terms of perceptual learning: Since normally, because of acuity limitations, the only information available in parafoveal vision concerns low-resolution features of letters; even when magnification provides better information, readers are unable to make use of it.

Adult↗
PubMed1992

Effects of lateral masking and spatial precueing on gap-resolution in central and peripheral vision.

The data made available by this experiment add two points to the information obtained by previous studies on eccentric vision and lateral masking. First, they demonstrate a clear effect of target-mask similarity on visual gap-resolution in eccentric vision: increasing target-mask similarity systematically decreases resolution performance. Second, spatial precueing has no effect on gap-resolution performance. One implication of this experiment is that with the present stimulus configurations, visual resolution should decrease much more strongly with eccentricity than it does with classical isolated or bar-masked optotypes.

Humans↗
PubMed1992

Letter visibility and word recognition: the optimal viewing position in printed words.

It has repeatedly been shown that the time and accuracy of recognizing a word depend strongly on where in the word the eye is fixating. Word-recognition performance is maximal when the eye fixates a region near the word's center, and decreases to both sides of this "optimal viewing position." The reason for this phenomenon is assumed to be the strong drop-off of visual acuity: the visibility of letters decreases with increasing eccentricity from fixation location. Consequently, fewer letters can be identified when the beginning or ending of a word is fixated than when its center is fixated. The present study is a test of this visual acuity hypothesis. If the phenomenon is caused by letter visibility, then it should be sensitive to variations of visual conditions in which the letters are presented. By increasing the interletter distances of the word (e.g., a_t_t_e_m_p_t), letter visibility was decreased. As expected from our hypothesis, the viewing-position effect became more exaggerated. An additional experiment showed that destroying word-shape information (e.g., aTtEmPt) decreased overall word-recognition performance but had no influence on the viewing-position effect. Varying the viewing position in words might thus be used as a paradigm, allowing one to separate out the contribution of letter information and supraletter information to word recognition.

Adult↗
PubMed1991

The effects of target discriminability and retinal eccentricity on saccade latencies: an analysis in terms of variable-criterion theory.

Two experiments are reported that studied changes in saccade latencies (SLs) in a target-identification task as a function of target discriminability and eccentricity. SLs were found to be longer when target discriminability was low and eccentricity was large, both factors showing a significant interaction. Variable-criterion theory (Grice, 1968) was used to derive a working model of the perceptual and decisional processes influencing SLs in the present task. Application of the measurement operations of the theory provided a good quantitative description of individual SL distributions. The analyses in terms of variable-criterion theory suggest that the perceptual process influencing SLs starts earlier and operates at a faster rate when the saccade target can be discriminated on the basis of global-visual features (e.g., size) than when local features (e.g., gaps) have to be extracted.

Adult↗
PubMed1991

On the role of refixations in letter strings: the influence of oculomotor factors.

Recent studies of reading and word recognition have shown that eye-movement behavior depends strongly on the position in the word that the eye first fixates; the probability of refixating in a word is lowest with the eye near the middle of the word, and it increases as the eye fixates to either side. It has generally been assumed that the cause for this optimal landing position phenomenon lies in the very strong drop-off of visual acuity even within the fovea; refixation should be more likely when the eye starts from a noncentral position, because here less information can be extracted during one fixation. It may, however, be the case that the phenomenon is caused not by acuity drop-off, but by differences in within-word oculomotor scanning tactics as a function of the position that the eye initially fixates. To test this, in the present experiment we kept visual information constant while we varied the initial fixation position. We used homogeneous strings of letters of different length. One letter in each string was different from the rest (e.g., kkkkkok), and this was the letter that the subject initially fixated. This target letter had to be identified before saccading to a comparison string. The position of the target letter in the string was varied from trial to trial. If, owing to acuity limitations, refixations reflect insufficient information extraction, then, because the target letter is always directly fixated, the pattern of refixations in this condition should be independent of the first fixation position. However, the obtained refixation probability showed a strong dependence on the position of first fixation. The number of refixations was independent of the absolute length of the letter strings, but it seemed to be influenced by the proportion of the string over which the eye had to pass. The larger this proportion, the higher the probability of refixation. The results suggest that to a certain extent refixations in letter strings (or words) reflect properties of the oculomotor system rather than visual information extraction.

Adult↗
PubMed1990

Some results on translation invariance in the human visual system.

Four experiments were conducted to study the nature of visual translation invariance in humans. In all the experiments, subjects were trained to discriminate between a previously unknown target and two non-target distractors presented at a fixed retinal location to one side of the fixation point. In a subsequent test phase, this performance was compared with the performance when the patterns were presented either centrally at the fixation point or at a location on the other side of the fixation point, opposite to the location where the patterns were learned, but where acuity was identical to what it was at the learned location. Two different experimental paradigms were used. One used an eye movement control device (Experiment 1) to ensure the eye could not move relative to the patterns to be learned. In the other three experiments, presentation duration of the patterns was restricted to a short enough period to preclude eye movements. During the training period in Experiments 1 and 2, presentation location of the patterns was centered at 2.4 deg in the periphery, whereas in Experiments 3 and 4 presentation eccentricity was reduced to 0.86 and 0.49 deg. In all four experiments performance dropped when the pattern had to be recognized at new test positions. This result suggests that the visual system does not apply a global transposition transformation to the retinal image to compensate for translations. We propose that, instead, it decomposes the image into simple features which themselves are more-or-less translation invariant. If in a given task, patterns can be discriminated using these simple features, then translation invariance will occur. If not, then translation invariance will fail or be incomplete.

Discrimination Learning↗