Icelandic norms for the Snodgrass and Vanderwart (1980) pictures: name and image agreement, familiarity, and age of acquisition.

This paper presents Icelandic norms for the widely used pictorial stimuli of Snodgrass and Vanderwart (1980). Norms are presented for name agreement, familiarity, imageability, rated and objective age-of-acquisition (AoA) of vocabulary, and word frequency. The ratings were collected from 103 adult participants while the objective AoA values were collected from 279 children, 2.5-11 years of age. The present norms are in many respects similar to those already collected for other language groups indicating that the stimuli will be useful for further psychological studies in Iceland. The rated AoA values show a high correlation with objective AoA (r = 0.718) thus confirming previous studies conducted with English speaking participants that rated AoA is a relatively valid measure of objective AoA. However, word frequency and familiarity are more closely correlated with rated AoA than with objective AoA indicating that these factors play some role in the ratings. Objective AoA norms are therefore to be preferred in studies of cognitive processes.

Speech segment durations and quantity in Icelandic.

Icelandic has a phonologic contrast of quantity, distinguishing long and short vowels and consonants. Perceptual studies have shown that a major cue for quantity in perception is relational, involving the vowel-to-rhyme ratio. This cue is approximately invariant under transformations of rate, thus yielding a higher-order invariant for the perception of quantity in Icelandic. Recently it has, however, been shown that vowel spectra can also influence the perception of quantity. This holds for vowels which have different spectra in their long and short varieties. This finding raises the question of whether the durational contrast is less well articulated in those cases where vowel spectra provide another cue for quantity. To test this possibility, production measurements were carried out on vowels and consonants in words which were spoken by a number of speakers at different utterance rates in two experiments. A simple neural network was then trained on the production measurements. Using the network to classify the training stimuli shows that the durational distinctions between long and short phonemes are as clearly articulated whether or not there is a secondary, spectral, cue to quantity.

The role of F1 in the perception of voice onset time and voice offset time.

An important speech cue is that of voice onset time (VOT), a cue for the perception of voicing and aspiration in word-initial stops. Preaspiration, an [h]-like sound between a vowel and the following stop, can be cued by voice offset time, a cue which in most respects mirrors VOT. In Icelandic VOffT is much more sensitive to the duration of the preceding vowel than is VOT to the duration of the following vowel. This has been explained by noting that preaspiration can only follow a phonemically short vowel. Lengthening of the vowel, either by changing its duration or by moving the spectrum towards that appropriate for a long vowel, will thus demand a longer VOffT to cue preaspiration. An experiment is reported showing that this greater effect that vowel quantity has on the perception of VOffT than on the perception of VOT cannot be explained by the effect of F1 frequency at vowel offset.

Auditory and linguistic factors in the perception of voice offset time as a cue for preaspiration.

Previous research [J. Pind, Acta Psychol. 89, 53-81 (1995)] has shown that preaspiration in Icelandic, an [h]-like sound inserted between a vowel and the following closure, can be cued by Voice Offset Time (VOffT), a speech cue which is the mirror image of Voice Onset Time (VOT). Research has also revealed that VOffT is much more sensitive to the duration of the neighboring vowel than is VOT [J. Pind, Q. J. Exp. Psychol. 49A, 745-764 (1996)]. This paper explores the hypothesis that it is primarily the perceived quantity of the vowel that is responsible for the effect of the vowel on the perception of preaspiration. This hypothesis is based on the linguistic fact that preaspiration can only follow a phonemically short vowel. This linguistic hypothesis is contrasted with an auditory hypothesis in terms of forward masking. Perceptual experiments show that the perceptual boundaries for preaspiration can be affected either by changing the preceding vowel's duration or its spectrum. If the spectrum of the vowel changes towards that of a long vowel, longer VOffT's are needed for listeners to perceive preaspiration, thus lending support to the linguistic hypothesis.

Advances in dyslexia research.

Dyslexia: Advances in theory and practice, Dyslexia Research Foundation and Center for Reading Research, 20-23 November 1997, Stavanger, Norway.

Rate-dependent perception of aspiration and pre-aspiration in Icelandic.

Speech segments are highly context-dependent and acoustically variable. One factor that contributes heavily to the variability of speech is speaking rate. Some speech cues are temporal in nature-that is, the distinctions that they signify are defined over time. How can temporal speech cues keep their distinctiveness in the face of extrinsic transformations, such as those wrought by different speaking rates? This issue is explored with respect to the perception, in Icelandic, of Voice Onset Time as a cue for word-initial stop voicing, word-initial aspiration as a cue for [h], and Voice Offset Time as a cue for pre-aspiration. All the speech cues show rate-dependent perception though to different degrees, with Voice Offset Time being most sensitive to rate changes and Voice Onset Time least sensitive. The differences in the behaviour of these speech cues are related to their different positions in the syllable.

Spectral factors in the perception of vowel quantity in Icelandic.

Previous research has shown that the ratio of vowel to rhyme (vowel + consonant) duration is a major cue for quantity in Icelandic. In particular it serves as a higher-order invariant which enables the listener to disentangle those durational transformations of the speech signal which are "extrinsic" (e.g. due to changes in speaking rate) from those which are "intrinsic" to the phonemic message, involving a change of phonemic quantity. Previous research has been based on speech segment contrasts which are purely durational, involving vowels with a uniform spectrum whether phonemically long or short, such as [a] or [I]. This paper looks at the role of spectral factors in vowels which are spectrally dissimilar in their long and short varieties. It is shown that in these cases the spectral differences can be sufficiently great to override the previously established relational invariant for quantity. The implications of this finding for a model of quantity perception are discussed.

Constancy and normalization in the perception of Voice Offset Time as a cue for preaspiration.

It is a well-established fact that the realization of individual speech segments is heavily dependent on context. One factor, temporal organization, has been shown to affect numerous speech cues, especially those which are defined in the temporal domain. Theories of speech perception have adopted two different views of the nature of these contextual effects. On the one hand it has been hypothesized that the listener normalizes by taking account of the context. On the other hand it has been hypothesized that higher-order invariants, e.g. speech segment ratios, are sufficient cues for the relevant temporal contrasts, thus obviating the need for mechanisms of normalization. The present series of experiments investigates the merits of these opposing theoretical positions. The experiments involve Voice Offset Time as a cue for preaspiration in Icelandic. The results indicate that durational ratios can, for the most part, function as higher-order invariants for the perception of preaspiration.

Speaking rate, voice-onset time, and quantity: the search for higher-order invariants for two Icelandic speech cues.

The temporal structure of speech has been shown to be highly variable. Speaking rate, stress, and other factors influence the duration of individual speech sounds. The highly elastic nature of speech would seem to pose a problem for the listener, especially with respect to the perception of temporal speech cues such as voice-onset time (VOT) and quantity: How does the listener disentangle those temporal changes which are linguistically significant from those which are extrinsic to the linguistic message? This paper reports data on the behavior of two Icelandic speech cues at different speaking rates. The results show that manipulations of rate have the effect of slightly blurring the distinction between unaspirated and aspirated stops. Despite great changes in the absolute durations of vowels and consonants, the two categories of syllables--V:C and VC:--are nonetheless kept totally distinct. In two perceptual experiments, it is shown that while the ratio of vowel to rhyme duration is the primary cue to quantity and remains invariant at different rates, no such ratio can be defined for VOT. These results imply that quantity is the only one of these two speech cues that is self-normalizing for rate. Models of rate-dependent speech processing need to address this difference.