Morton, Marcus, and Frankish (1976) defined "perceptual center," or "P-center," as a neutral term to describe that which is regular in a perceptually regular sequence of speech sounds_ This paper describes a paradigm for the determination of P-center location and the effect of various acoustic parameters on empirically determined P-center locations, It is shown that P-center location is affected by both initial consonant duration and, secondarily, subsequent vowel and consonant duration, A simple two-parameter model involving the duration of the whole stimulus is developed and gives good performance in predicting P-center location. The application of this model to continuous speech is demonstrated. It is suggested that there is little value in attempting to determine any single acoustic or articulatory correlate of Pcenter location, or in attempting to define P-center location absolutely in time. Rather, these results indicate that P-centers are a property of the whole stimulus and reflect properties of both ~he production and perception of speech.

1. We studied the effect of dark adaptation on the spatial organization of receptive fields of single cells in the lateral geniculate nucleus l.g.n. of the cat. 2. Contrary to previous reports, we found that in many l.g.n. cells the ability of the receptive field surround to suppress the response of the centre was diminished following dark adaptation. 3. The degree of reduction of the surround antagonistic strength varied from cell to cell, and was independent of the various classifications of visual neurones (X/Y, ON/OFF, layer, A/layer, A1 and central/peripheral). 4. Most cells also showed an increase in the apparent size of the excitatory centre upon dark adaptation. On the average, the width of the most effective bar stimulus located at the centre of the receptive field increased more than twofold. 5. We also studied the effect of dark adaptation on the temporal properties of l.g.n. receptive fields. In many cells dark adaptation changed the temporal modulation transfer function: it flattened the amplitude function, and changed the phase relationship between the centre response and the surround response. 6. Retinal ganglion cells showed qualitatively similar behaviour to that of l.g.n. neurones. 7. Our data do not support the notion that retinal ganglion cell centres converge on l.g.n. cells to form their surround mechanism.

The stimulus suffix paradigm has been used to establish the importance of precategorical acoustic storage (PAS) as a theoretical construct in the investigation of attention and speech perception. Morton and Chambers concluded that sounds must have typical "speechlike" properties extracted at an early stage of processing in order to act as suffixes.

Morton & Chambers (1976) showed that the suffix effect ‐ a selective impairment in serial recall on the final serial position of an acoustically presented list ‐ was crucially affected by whether the suffix was a speech sound or a non‐speech sound. They also claimed that the classification of a sound as speech‐like was determined simply by the acoustic properties of the sound and not at all by the context. The crucial sound in their experiments was a steady state, naturally produced vowel sound which failed to give a suffix effect. We report here that when the sound was the only suffix used, it did produce a suffix effect. We conclude that, contrary to Morton & Chambers' conclusion, context effects are indeed operative in determining whether a sound produces a suffix effect.

Abstract.In articulatory phonetics speech is described as a sequence of distinct articulatory gestures, each of which produces an acoustic event that should approximate a phonetic target. Due to the overlap of the gestures these phonetic targets are often only partly realized. Atal (1983) has proposed a method for speech coding based on so-called temporal decomposition of speech into a sequence of overlapping target functions and corresponding target vectors. The target vectors may be associated with ideal articulatory positions. The target functions describe the temporal evolution of these targets. This method makes no use of specific articulatoty or phonetic knowledge. We have extended and modified this method to improve the determination of the number and the location of the target functions and to overcome the shortcomings of the original method. With these improvements temporal decomposition has become a strong tool in analysing speech, from which researchers working on speech coding, recognition and synthesis may profit.Zusammenfassung. In der ~. tikulatorischen Phonetik wird die Sprache als eine Folge einzelner Artikulationsgesten beschrieben, die jeweils ein akustisehes Ereignis zur Folge haben, das eine Ann~iherung an ein phonetisches Ziel darstellt. Aufgrund der Oberlappung der Gesten werden diese phonetisehen Ziele oft nut teilweise verwirklicht.Atal (1983) hat eine Methode zur Sprachcodierung vorgeschlagen, die auf der sogenannten Temporalen Dekomposition der Spraehe in eine Folge von iiberlappenden Zielfunktionen und den entsprechenden Zielvektoren beruht, Die Zielvektoten kOnnen idealen Artikulationsstellungen zugeordnet werden. Die Zielfunktionen beschreiben den zeitlichen Entwicklungsverlauf dieser Ziele. Bei dieser Methode werden keine spezifischen Artikulations-oder Phonetik-Kenntnisse angewendet. Wir haben die Methode erweitert und abge~indert, um die Bestimmung yon Anzahl und Position der Zielfunktionen zu verbessern und die Naehteile der urspriinglichen Methode zu umgehen. Durch diese Verbesserungen wurde die Temporale Dekomposition zu einem wertvollen Hilfsmittel in der Sprachanalyse, wovon Forschungen in der Sprachcodierung, -erkennung und -synthese profitieren werden.R~sum~. En phon~tique articulatoire, la parole cst d~crite comme ~tant une s~quence de gestes articulatoires distincts. produisant un ~v~nement acoustique qui devrait se rapprocher d'une cible phon6tique. Du fait du recouvrement des gestes, ces cibles phon6tiques ne sont souvent atteintes qu'en partie.Atal (1983) a propos6 une m6thode permettant le codage de la parole, bas6e sur ce que I'on appelle la d6composition temporelle de la parole en une s6quence de fonctions-cibles de recouvrement et de vecteurs-cibles correspondants. Les vecteurs-cibles peuvent 6tre associ6s ~ des positions articulatoires id6ales. Les fonctions-cibles d~crivent l'6volution temporelle de ees cibles. Cctte m6thode ne requiert pas de connaissances articulatoires ou phon6tiques particuli~res. Nous l'avons 61argie et modifi6e pour mieux d6terminer le nom...