Not a native speaker, but this is still wrong, Hiragana is just like Katakana, each character is a syllable (more or less, n is a bit special in both sets). There's a 1:1 mapping between Hiragana, Katakana and syllables that exist in Japanese.
Kanji (Chinese-style characters) aren't phonetic on the other hand, they map to several different sounds, and several Kanjis may map to the same sound (not necessarily a single syllable).
To contest your point of a 1:1 mapping, there are hentaigana which are older than the obsolete characters in both hiragana and katakana. Interestingly enough, these are not supported in Unicode.
Additionally, depending on context, hiragana might not have a phonological reading. See the object marker 'wo'. Katakana is usually phonological, except for the same usage of object marker.
In summary, someone who says "Hiragana can form pictures but Katakana can only form sounds" is either a philosopher who practices calligraphy or misinformed.
> To contest your point of a 1:1 mapping, there are hentaigana which are older than the obsolete characters in both hiragana and katakana.
Technically yes, but they don't matter. The modern hiragana and katakana syllabaries have intentional symmetry. Anything written in one can be written in the other, and is (stylistic unorthodox choices of syllabary, old or limited computers where only one set is available, Japanese Braille which makes no such distinction, etc.)
> Additionally, depending on context, hiragana might not have a phonological reading.
This can also be true of katakana in some situations.
The chōonpu (long vowel marker) can be used for hiragana too, but it's not how words are usually spelled. Likewise, you can use hiragana-style long vowels in katakana.
From a historical perspective, it's not true. Both types of kana were derived from Han characters, often the same characters, in different ways. Their usage has varied over time.
As for the neurological claim, I did a quick search and found an article which cited:
> Uno (as cited in Itani 2001) and Saito (as cited in Kosaka & Tsuzuki) say that kana is primarily processed phonologically in the reading process, whereas kanji is processed semantically.
It's a bit poetic but it's almost right: Hiragana is for words (native Japanese) and Katakana is for spelling things out phonetically (onomatopoeic words and foreign loanwords).
This ignores the fact that a significant percentage of everyday Japanese life is now loanwords, so you can't really dismiss them as not being part of the language.
I'm absolutely not qualified to address this definitively, but my understanding is that Hiragana is typically used for verb conjugations, adjective inflections, particles (like "の" for indication of possession for example), some natively Japanese words where no one really uses the Kanji for whatever reason, and some other stuff that's similar in nature. Katakana is typically used for writing foreign words so that they use the pronunciation rules of Japanese (like "コカ・コーラ" for Coca-Cola for example) and onomatopoeias.
This writing is sort of a strange metaphor, but I guess the point the author makes is that kanji can be transliterated as hiragana but not katakana. The writer goes on to talk about traumatic brain injuries so I guess he's aiming at the cultural value of each syllabary.
I'm not a native speaker, but if I were to make an equally strange metaphor as the author, katakana feels like writing in all capital letters.
Kanji can be transliterated either way, and both forms are lossy since there are so many homonyms and kana only encodes sounds. It's traditional to annotate difficult Kanji pronunciation with small Hiragana called Furigana, for example in children's books. But it could be done all the same in Katakana. Modern Chinese words that Japanese borrows are usually translated in Katakana for example.
Kana mostly contain just sounds, but do contain some morphological information—there are homonyms in kana as well, after all. This is a bit rare, however.
That sounds really weird to me. Does that sound right to any native Japanese speakers here?