Amodal Aspects of Linguistic Design

All spoken languages encode syllables and constrain their internal structure. But whether these restrictions concern the design of the language system, broadly, or speech, specifically, remains unknown. To address this question, here, we gauge the structure of signed syllables in American Sign Language (ASL). Like spoken languages, signed syllables must exhibit a single sonority/energy peak (i.e., movement). Four experiments examine whether this restriction is enforced by signers and nonsigners. We first show that Deaf ASL signers selectively apply sonority restrictions to syllables (but not morphemes) in novel ASL signs. We next examine whether this principle might further shape the representation of signed syllables by nonsigners. Absent any experience with ASL, nonsigners used movement to define syllable-like units. Moreover, the restriction on syllable structure constrained the capacity of nonsigners to learn from experience. Given brief practice that implicitly paired syllables with sonority peaks (i.e., movement)—a natural phonological constraint attested in every human language—nonsigners rapidly learned to selectively rely on movement to define syllables and they also learned to partly ignore it in the identification of morpheme-like units. Remarkably, nonsigners failed to learn an unnatural rule that defines syllables by handshape, suggesting they were unable to ignore movement in identifying syllables. These findings indicate that signed and spoken syllables are subject to a shared phonological restriction that constrains phonological learning in a new modality. These conclusions suggest the design of the phonological system is partly amodal.

straight path -->| straight path -->| Note: All features are noted in the order in which they appear. "H2" refers to the nondominant, neutral hand. All palm-orientations are given from the perspective of the signer. Palm--orientations listed as "dominant" or "non--dominant" refer to a palm--orientation facing the dominant or non--dominant sides of the signing space, such that if a signer is right--handed "dominant" refers to "right." |--> refers to movements directed away from the place of articulation; -->| refers to movements directed toward the place of articulation; |-->| refers to movements directed away from the first place of articulation towards the second place of articulation; --> refers to movements that occur at the place of articulation and neither move away from or towards it.     If you are shown a sign with one recognizable part, please press one. If you are shown a sign with two recognizable parts, please press two. It is important to remember that although you may sign certain words differently than the signer in the video, your decisions should be based on the way the signer is producing the stimulus. That having been said, please watch the video closely. In the second portion of this experiment the task will be the same as in the first. The only difference is that the signs shown to you in the video will not be real ASL signs. Instead, they are signs carefully crafted to look similar to that which appear in ASL. This is inconsequential; your task is the same. If you see a sign with one part, please press one. If you see a sign with two parts, please press two. In the second portion of this experiment the task will be the same as in the first. The only difference is that the signs shown to you in the video will not be real ASL signs. Instead, they are signs carefully crafted to look similar to that which appear in ASL. This is inconsequential; your task is the same. If you see a sign that appears to be simple, please press one. If you see a sign that appears to be complex, please press two.

Appendix S2: The instructions presented to English speakers.
In this experiment, we ask you to judge some signs in American Sign Language. There are several different types of signs in American Sign Language, and your job will be to determine which type you see. The experiment as a whole has two large sections, each with multiple parts. Section 1: syllable count condition Some signs have one chunk whereas others have two. To use an example from English: The word "sport" has one chunk, while "support" has two. Please note that those chunks have no specific meaning, but we still perceive that "sport" has one chunk whereas "support" has two. Likewise, signs in American Sign Language may have either one chunk or two. We would like to find out whether English speakers can perceive this. In addition to having different numbers of chunks, words can vary in how many pieces of meaning they have. Even in words with multiple pieces of meaning, you can still perceive different numbers of chunks. To use examples from English, the word "sports" has two pieces of meaning-the "sport" part and the plural part "-s". Likewise, "supports" includes the base "support" and a plural "--s". For your task here, however, the pieces of meaning are irrelevant. Only pay attention to how many chunks each word has: "Sports" is only one chunk, while the word "supports" has two meaningless chunks.

Real words
First you will practice the task with English words before moving on to American Sign Language. In each trial you will see one word. Your task is to determine whether this word has one chunk or two. If it has one chunk, press 1; if it has two, press 2. Please respond as fast and accurately as you can-don't try to over-analyze; just go with your gut feeling. Any questions? Please press "z" to continue.
[participants receive the English practice] Now for the American Sign Language practice. Like the English examples, these signs have either one chunk or two. We want to see whether you can guess how many are in each sign. Please watch the signer carefully and judge the signs exactly as they appear in the video. As before, in each trial you will see one word. Each word is a real word in American Sign Language. If the sign has one chunk, press 1; if it has two, press 2. We know this is a hard task without knowing American Sign Language. Please try as best as you can. Any questions? Please press "a" to continue.
[participants receive the ASL practice] Good job on the practice! Now for the main part of the experiment. Your task is the same as in the practice: please determine if each sign has one chunk or two. Any questions? Please press "q" to continue.
[participants receive the ASL word syllable condition] Novel words Thank you very much! Now we move to the second part of the experiment. This part is very similar to the previous one, except that the signs you will see now are new-they do not actually exist in American Sign Language, but we think they are possible signs. We ask you to determine whether they include one chunk or two. To explain what we mean, let's practice with similar examples from English. In this practice, you will see nonsense English words. As before, do not base your answer on how many pieces of meaning the word might have. If the word has one chunk, press 1; if it has two, press 2. Please respond as fast and accurately as you can-don't over--analyze; just go with your gut feeling. Any questions? Please press "e" to continue.